Can't keep you up very well how? Are they running oom? Are you taking too much damage too fast, basically being gibbed in a short time? Phase 2 basically needs pure spam heals until you hit phase 3. Have everyone save their dps trinkets/heroism/whatever for phase 2 to get him out of that mode asap.
Chugging an armor pot or two wont hurt either.
You'll be blocking a bunch when he starts to dual wield and getting crazy threat from holy shield. Phase 2 is the time for dps to go balls to the wall. (And phase 3 of course. Having a room full of infernals is bad juju)
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