Phantoms don't look at player when using "facing entity" in commands

When teleporting phantoms to face a player, they invert the vertical looking direction.

Can be replicated by using a command such as the command listed below in a repeating command block. 

execute as @e[type=phantom] at @s run tp @s ~ ~ ~ facing entity @p

You will see the looking direction of the phantom vary opposite of the vertical height of the player in relation to the phantom.