The spell is available for wizards and undead. So if a PC is not a Wizard but is an undead character, like say a Hallow, would this become available? Like maybe a Bard levels up and gets an empty 3rd level spell slot. This spell isn't on the Bard's spell list, but the wording suggests that our undead Bard friend can select this.

The spell is available for wizards and undead.

The Undead is a specific Warlock patron for whom this is on the Expanded Spell List. Being undead has nothing to do with it, and an undead character couldn't cast it unless they were a Wizard or a Warlock with The Undead as a patron. 

Oooooh the Undead Patron, that makes perfect sense.

I think the speed needs to be higher. Elite athletes run marathons at around 13 miles an hour. 

Honestly, Free Horse sounds great. 

Might even be worth taking the Ritual Caster Feat for this spell, depending on your Character. 

Quote from DK275 >>

I think the speed needs to be higher. Elite athletes run marathons at around 13 miles an hour. 

While it's not fast compared to real world horses, (about 11 mph walking speed and 22 mph dashing), 200 feet per round is super fast for 5e. For context, an adult or ancient dragon using legendary actions to Wing Attack and its action to dash can just barely match 200 feet. Very few other creatures come close to that, and even fewer can match or beat that.

For a 3rd level spell that you can cast with just time, matching pace with ancient dragons going all out is pretty fast already. That said, if you do want it to go faster, pick up haste to double its speed and give it a second action to dash with. Then it'll be able to run 68 mph.

There is nothing in the rules saying you cant Ritual cast while traveling, so you can basically keep this horse up forever out of combat, as long as you take 10 minutes to travel at a normal speed. 

RAW you would summon another Horse and would have to switch, but ask your DM if he would be ok to just refreshg the current ones duration. 

So 200 feet per six seconds = 33.33 feet per second =22.7 mph, which is quite a bit larger than 13(the speed given for travel at a fast pace).

Only issue with this is that since it’s a third level spell, your dm would have to give it to you, you wouldn’t just get it with the feat, and also costs 150 gp to inscribe it

What I'd recommend is get a character in the party to be able to cast normally, then pool together party resources to get it shared around fast.

Interesting, it has the ritual tag here as it should - but on my (Warlock) character sheet it doesn't show it as a ritual anymore ... ?

For a 3rd level spell slot that disappears if it takes any damage, doesn't seem too OP to me.

Now, ritual casting it 4-5 times so everyone has one, and then re-doing the whole time while on the move = party that 'marches' at 13 miles per day (including up stairs), or at half speed across rough terrain/water - all with no worry about exhaustion. 

Or using 1-2 of them to pull a wagon, although the time (and skill) to hitch up the new 'horse' would hit you about every hour or so.

Kinda shitty to last just 1 hour. Unless you can maintain it while still mounted.

Bruh wtf why is it duration limited...

I just wanted a ritual mount for my Ritual Caster Eldritch Knight...

If only Find Steed was a ritual and wasn't paladin exclusive....

Eff it, i would rather homebrew one of them to be used by my Eldritch Knight as a permanent Ritual...

Edit:

btw beyond being a ritual spell, isn't it just plain worse than find steed ?

It has essentially one HP and can't even have the stats of a Warhorse, if you don't have mounted combatant it's basically useless in a fight.

A level 5 wizard can cast this as a ritual 30 times over the course of an hour.

Each phantom steed takes on the stat block of a riding horse.

If every one of those 30 horses successfully landed an attack on a single target, they would deal 60d4+180 (if my math is right)

If they each rolled max damage, 30 horses can deal 420 damage to a single target in a single turn.

Quote from kiaten >>

A level 5 wizard can cast this as a ritual 30 times over the course of an hour.

No, PHB bottom pg 201 are ritual casting rules. Doing a spell as a ritual takes 10 minutes longer than non-ritual, so for a minute spell, that's effectively 11 minutes per cast.

Can Phantom Steed pull Drawn Vehicles such as a wagon?

if you cast spider climb on it, you can "skyrim" your steed up a mountain

Quote from YueOrigin >>

Bruh wtf why is it duration limited...

I just wanted a ritual mount for my Ritual Caster Eldritch Knight...

If only Find Steed was a ritual and wasn't paladin exclusive....

Eff it, i would rather homebrew one of them to be used by my Eldritch Knight as a permanent Ritual...

Edit:

btw beyond being a ritual spell, isn't it just plain worse than find steed ?

It has essentially one HP and can't even have the stats of a Warhorse, if you don't have mounted combatant it's basically useless in a fight.

The obvious answers here are:
a) It's not meant for combat, it's meant for traversal

b) It's a ritual spell, and as multiple people have pointed out you can cast while in motion, so the duration provides a negligible impediment to using the mount for travel, while also keeping the spell dispel-able.

c) Spells are not "balanced' across classes in the "perfectly equivalent" sense; Wizards can do a lot of things Paladins can't, and Paladins can do some things that Wizards can't. If you want to be a mounted magic knight with blaster powers and a magic horse, I'd say just go Oath of Glory.

It states that the spell ends of the steed takes damage.  It also says for the duration you can ride.  So once spell ends you can't ride it any more. So it basically takes damage and let's you get off. RAW