Except that you literally cannot do that.
In the first phase he just initiates dialogue if you get his health low enough so that you could potentially kill him with Anathema, and it does nothing useful if you hit him with it before then. What a piece of junk.
In the second phase, he teleports across the map so you can't actually move him to the middle of your team, and and his buddy fills your starting position full of AoE pain so you have to spread out, which doesn't matter because you still get stomped into the ground anyway, and even if you somehow manage to get to a point where you can get near him to teleport him, his void glide teleport will be back up, even if does have a cooldown longer than 1 turn.