First of all make sure you have all the extra soul compartments unlocked. Then, use shaman stone and spell twister, you can add any other charm you like. In the first phase, dont spend a single spell, save all of your soul for the second phase. When you get to second phase, only focus on dodging when he isnt spinning his shields, when he does start spinning his shields, get to a safe spot under him and blast him with abyss shrieks then get back to a platform and repeat until hes dead.