Totally stuck on the 2nd act boss

I may be the worst gamer in the history of games, but I have been so stuck on the 2nd act boss, that I am considering just not playing poe2 anymore (I cannot continue the campaign honestly).

I am playing a lvl 38 cold sorc. I have pump my lightning resistance to cap it (the yellow lightning do no damage to me). However, I have only made it to phase 2 once. All my other tries I have run out of red flasks, and not even a fourth of his life was missing.

My approach is to circle him, drop Hypothermia, and frost bombs. I dodge his spears, and I shoot frost bolts at him to freeze him when I can. But his life pool is HUGE, and even if I manage to avoid most of his attacks, I get hit every now and then, specially when he calls his minions during the sand storm (I cannot kill them fast enough that they don't hit me).

I am so frustrated. I have not been that frustrated while playing, and I love all the Dark Souls games (my favourite games). This is just so weird :(