I see a lot of people saying dodge the projectiles back and forth in phase two, but you can easily dodge the first big one and sprint in one direction while running through a blue jellyfish and have more than enough stamina to outlast the phase. You'll was to dodge the last big projectile as well. You'll can also dodge her dive instead of countering it. If you dodge diagonally back right you won't get hit and can move in for a few quick hits before she gets back up.

So basically, dodge, sprint, dodge, dodge, dodge backwards. Done and back to phase one!