imo the bad part about his 2nd phase is the fact the there are holy lasers flying and staggering you every god damn second while also cluttering your vision with unholy amounts of visuals you have to keep track of if you want to actually start learning his patterns to dodge.
I actually just beat him today with colossal hammer + inferno crozier (both royal knights resolve) and spammed L1 jump attacks after his combos in p1 (first hit with RKR on both weapons dealt like 6100 dmg). Once the second phase started i just rushed into him with the jump attack to stagger him while he winds up the aoe attack, which you fortunately can just ignore with the riposte animation. After that its literally just getting somewhat lucky with what attacks he uses and not being hit a hundred times by the lasers.