To anyone coming to this thread in posterity: Short version:
Corrosive + blast is your friend for phase 1. High crit sniper should do it. Jump to the platform way up above to the right of where you enter his area, he'll come up and poke his head through the platform. Rhino, keep Roar up, wait for him to do his little alarm thingy and you should be able to get 3-4 shots in, rinse repeat, you won't take any damage up there. Slow and a bit annoying but easy.
Shattering Impact Melee with decent crit stacks ( blood rush + gladiator rush + berserker for instance ) is your friend for phase