So, for most of my campaigns (I currently run three and in the past have run several at once) I limit access to sources when creating characters and levelling up. When I know I have new players in a group...which is most of the time...I find that limiting things to just Player's Handbook allows the newer players not to be overwhelmed by all the massive number of options. Kind of taking a fundamentals approach. Learn the basics then we can expand. For such games I usually open out spells and feats to XGtE and TCoE once the new players hit around level 6 or so. By that point they've learnt the basics, we've usually covered all of the inconsistencies in the rules as written and interpreted them for our table.

Recently though a player has brought up that they felt a bit hemmed in by this approach. Now granted they were playing a class/subclass that I'd made an exception for and allowed them to play despite not appearing in PHB. This has me sort of reassessing the approach I've traditionally taken. Is the spell list in PHB too restrictive (as a veteran of pre 5e and many other TTRPG systems I don't believe it is)?

So I guess my question is what are other DM's experiences of limiting sources for your game/campaign? Do you do it? Do you think it's a good idea when new players are in the mix? Would you open out the other options at higher/lower levels?

It isn't necessarily a bad idea to limit the source to just the players hand book for new players learning the game, for it keeps all the information in one easy access spot. Yet not every new player is going to be the same, some like you have mention are interested in using the other books. I wouldn't limit them to just the players handbook, if they have profound interest in using the other books. 

Some games i run uses all published books, others limit source materials for a vaeriety of reasons. I also don't usually allow Unearthed Arcana or third-party material without approval.

My campaigns that limit sources are generally setting specific, or to prevent having too many options such as plethora of feats, spells or unusual races. I also tend to prevent setting-specific races to other settings.  It may also serve to dial down power level when using published adventures as written.  

There's nothing wrong with limiting source material, even Adventurer's League Organized Play did so.

My current DM lets us use any WotC published material. No UA, homebrew or 3rd party. Personally, I do the same. It’s never been a problem. 
That said, confining new players to the PHB makes a lot of sense. The number of choices otherwise can be overwhelming. But I would try to steer them away from some of the more lackluster PHB options. Or if they really wanted to play a beastmaster, I’d probably tell them to use Tasha’s. Or Fizban’s dragonborn.

I think limiting to the PHB is too restrictive. Also, for players like me, it creates another issue: While I know almost all classes, races, feats and spells by heart, I sometimes do not remember from which book a spell is from. This particularly comes up with Xanathar spells, as many of them nowadays are staples for most characters - like Toll the Dead or Absorb Elements. It might also be an issue for new players who use certain online resources other than D&D Beyond for their charcters, where they have all official options listed, but without them being sorted by books.

Also, the lack of blade cantrips is a severe hit for melee clerics, melee sorcerers and Eldritch Knight fighters.

I generally like to limit things to just the core 3, Xanathar’s and Volo’s Guides, and my own homebrews. It’s rarely been an issue and if someone approaches me and says they really, really want to play something from another source I consider it on a case by case basis and usually approve it with the exception of many other homebrews that I haven’t personally written, and even then I try to work with the player to tweak it rather than just refusing their request. So I guess you could say I sortakinda limit things, or that I limit things until I don’t, but those exceptions are not very common as most of the time the players just roll with it.

PS- It helps that I’m the person with all the books.  

There are well over 10 different books with additional content for PCs, weather, classes, subclasses, feats, spells, etc. That makes keeping track of it all “difficult” for everyone. So yes feel free to limit what your players have access to. I limit it to the books I have and the few subclasses/classes I have homebrewed. Further I typically limit it to: PHB, TASHA’s, XANTHER’s, and Fizban - especially for newer players. 

I don't allow UA or outside homebrew, and I tend to have source restrictions on either a hardline or case-by-case basis depending on my campaign. Personally, I feel if you want to limit a game to fewer choices, that's your prerogative. I do it for worldbuilding reasons. I've never done it because players were new, but all my new players have come in with a lot of D&D knowledge already, so it's never been an issue for me.

As for the PHB itself, there are a good number of choices in the PHB for casters, but it definitely has some lackluster options for certain martial classes - ranger and monk, specifically. If I had my heart set on playing one of those and I were limited to PHB, I'd probably feel a little restricted and likely roll up another class. If you want to limit choices but still have some flair, variety and good subclasses available, PHB + Xanathar's is a nice wombo combo.

What does 'too restrictive' mean? You can have a totally functional game with only SRD content, let alone PHB, but it certainly will be more limited.

For a new player it might be best for their character to be limited to just the PHB, so that they aren't overwhelmed, but more experienced players shouldn't get overwhelmed so they should be allowed access to more material.

I've never played with UA or Homebrew - there is enough published material that such things really aren't necessary.

Quote from Farling >>

For a new player it might be best for their character to be limited to just the PHB, so that they aren't overwhelmed, but more experienced players shouldn't get overwhelmed so they should be allowed access to more material.

I've never played with UA or Homebrew - there is enough published material that such things really aren't necessary.

 So here's the issue I have with that distinction. It isn't really fair when you have a mix of experiences around the table.And I could see how saying to one player they can only use PHB, but saying to another, they can use XGtE or Fizbans could cause issues or a weird dynamic around the table.

I usually always have the same limits of source materials for all players if any, regardless of experience but i offer new players the choice to opt for a pregenerated character, the Basic rules or Player's Handbook if they prefer to choose from a smaller selection or not build one at all. For people not just new to 5E but to D&D in general, the first character is usually a pregen until they get a better grasp of the game and want to make one of their own creation.

Quote from martintheactor >>

Quote from Farling >>

For a new player it might be best for their character to be limited to just the PHB, so that they aren't overwhelmed, but more experienced players shouldn't get overwhelmed so they should be allowed access to more material.

I've never played with UA or Homebrew - there is enough published material that such things really aren't necessary.

 So here's the issue I have with that distinction. It isn't really fair when you have a mix of experiences around the table.And I could see how saying to one player they can only use PHB, but saying to another, they can use XGtE or Fizbans could cause issues or a weird dynamic around the table.

 
It isn’t a matter of telling one player that they “can only use the PHB.” It’s a matter of simply handing them the book and telling them to pick a race and a class. It’s not a matter of restricting someone’s choices, it’s a matter of enabling them to make a choice.

Rather than limiting books, it would probably be a lot more fun for them if you just walked them through character creation and level up choices.  Rather than have them look though all the options, even if you limit them, it's going to be much faster and enjoyable if you ask what they are going for with their character, and then you give them suggestions to look at.  There are also plenty of new players that who would not only no be overwhelmed by the options, but enjoy looking through everything.

For new players limiting options isn't nearly as helpful as just doing character creation with them so you can guide them.  Limiting books is really just going to limit subclass/races/ feats/spells, but it's not going to help them avoid potentially confusing and knowledge intensive classes like druid, artificer etc that have a much higher chance of overwhelming them than a single racial choice during creation.

Hell, limiting books could even potentially be more confusing depending on what resource they are using to look stuff up if you can't parse by source book.

Oh, I don’t tell them to read through it to pick, just leaf or maybe skim through it and pick whatever seems fun to them. As a DM I can make it work for them no matter what combo they decide on, and the character creation system is simple enough that once they pick a race and a class I can walk them through the rest of chargen in only a few minutes.

I limit books/material to the books I have. 

All of the information out there that is available is a LOAD of stuff. It's hard to keep track of and know how features would affect your campaign. 

Run a game you are comfortable with. It's ok to tell a player NO if you are unfamiliar with a race, subclass, or spell.