This bug allows the phantoms to dive underwater, from the sky and not take damage while in the water. The phantoms do not sink like other undead Mobs. They Swim. they are also not damaged by a conduit beacon even when only 3 -5 blocks away. They also do not take damage from being underwater
Environment
Java 8, Mac Book Pro OS: Catilina
Linked issues
duplicates 1
Comments 2
Phantom swimming underwater is MC-129348. Please create a separate ticket for the conduit issue.
I made a vidoe showing off what I think you're trying to say, and I hope it helps.
https://youtu.be/sQzEl1fqoZ8