This is essentially just MC-125252 except that it only affects phantoms attacking players at high elevations. I'm not sure what constitutes "high" elevations, but the behaviour is consistently bugged at about y=96, y=187 and y=256. It works fine for me at y=32 and below.

To be clear, the issue is that after phantoms swoop at the player, they are supposed to fly back up and gain some altitude before swooping at the player again. Instead, they just nosedive into the ground and hang around there doing a faceplant for awhile before eventually flying back up.

If you use "data get entity" to check the value of their AY tag (The y coordinate they are trying to hang around), you'll notice that it is above the player initially, goes up (For some reason?) when they decide to attack the player, and goes down again after they swoop. In the case of high elevations, it goes too far down, as in far down below the ground too far, which is what's making them faceplant into the ground constantly, because they're trying to fly through it.