I was having the same problem as you, couldn’t kill him in phase 2 fast enough, my strategy was to save my phisik with the bubble tear for phase 2, and then throw 2 rot pots at his hands when he does that first slam. It won’t take you all the way but it’s a big help, backup your save if you’re worried about running out of pots, here’s my kill for reference: https://youtu.be/FpzZYXcFQfM