This is what me and my friends did: Kill all the enemies in the room without letting phogoth out. He'll break out if he takes damage, his minions can damage him and let him out. After you kill a certain number of enemies they stop spawning and you must let phogoth out. When you do stay grouped together and focus damage 1 enemy at a time. Once Xyro spawns one must run back to the door you entered from and go to the room before shrieker spawns. Have him stay there and have 2 with snipers go to back of map and focus fire on him. All the adds will be focused on guy in hallway but won't follow in. Do this till he is dead. We have lv 28 gunslinger warlock and 2 lv 27 defender titans