There was a time that phantoms keep getting stuck on ceilings. I wanted to check if mojang fixed it. They partly did, but it is not completely fixed. They will fly around like fish in the ocean, but they sometimes get stuck on walls. I made a video demonstrating it using a glass cage with tinted glass on top.

Edit: I thought they fixed the ceiling thing, but it is still not fixed. When I put myself in survival mode and then back to creative mode again, they still all fly to the top of the cage. You can see that on the picture I just added.