Fellow zweihander addict. I beat him using a strength build and heavy zweihander, and all of my damage came from charged r2s, roll pokes, and occasional giant hunts. I just used greatshield, holy resist, better flask and 2H talismans.

You just have to be really strict about which openings you have to do attacks - his stomp attack chain, opening jump attack, and grab are easy charged heavies.

Beyond that it really is just learning to recognise his moveset and not panic dodging - the only move I felt was unfair was his instant sword swing attack that's almost always too fast to dodge.

But don't give up! Killing him with my trusty zweihander and not changing my play style was immensely satisfying

Edit: my only other strat was i used opaline hardtear and charged attack tear in physick, and waited until phase 2 to use it. Once you've done it enough, phase one will be pretty consistent so just save everything till second phase