Best strategy I found for the normal version was to lock on and wait for him to try and hit you. Dodge to his left (your right) and then unlock and slash his leg a few times then back up to avoid his swipes/stomps. Re-lock on, then rinse and repeat. It works for both phases. You’re going to take some damage no matter what, but just try to not get greedy, stay patient, and you’ll be fine.