Teleport out of a grapple.

If you are grappled can you teleport out of it?

As long as the teleport doesn't require you to move, so the ones you'd generally think of will work, but things like teleport circle or transport via plants would not.

Yes - it’s important not to mistake Grappled for Incapacitated

You’re not being bear-hugged or pinned to the ground in a grapple - you’re just being stopped from moving and nothing more. You can still attack, cast spells, hurl profanities etc, etc.

And anything that takes either you or the grappler out of reach (such as teleport) ends the grapple.

Always pay close attention to what the rules say and what they don't say. Grappled says your movement speed is reduced to 0. That's it. It does not inhibit your ability to cast spells or use object that let you cast spells like magic rings, scrolls, etc. As long as the spell or ability you're using doesn't require you to move(such as to step through a portal), you can do it. So Misty Step, Misty Escape, Fey Step, Shadow Step, Teleport, Dimension Door all work. Arcane Gate, Teleportation Circle, Transport Via Plants, not so much.

I had to rule on this one. 

Player using Vortex Warp to get another player out of a Skeletal Slithering Bloodfin.

Vortex Warp

You magically twist space around another creature you can see within range. The target must succeed on a Constitution saving throw (the target can choose to fail), or the target is teleported to an unoccupied space of your choice that you can see within range. The chosen space must be on a surface or in a liquid that can support the target without the target having to squeeze.

Well, you could see him because the fish was just a skeleton so, "Sure, you can do that."