Once her heath drops far enough Phase 2 and 3 are similar in that D2R Items Vitaath summons ice clones , which render her immune to injury while they're active. Once they defeat them, her shield breaks, and she's vulnerable once more. Airborne AoE attack are also common during these phases. So players should be looking for highlighted areas in the stage that indicate where the damaging attacks will land.
Once her heath drops...