In the second phase, target the back right leg then keep really close to it, moving counter clockwise, it will break and allow a grievous attack and he won't hit you. You can run away, heal and repeat.
Ng+ his health and damages needs to be HEAVILY NERFED! My god I have 70 in vigor and he still 2 to 3 shots me. I do 3k dmg to his second phase and it's barely an inch of health gone. He's so fukkin op it's not even funny. Day 2 of trying to beat him and it's not workin.