I don't know how I did it (I don't even know how you get Super Sonic immediately without charging, nor how to unlock the camera from the boss) but when I got my first charge and stunned him, he didn't go down properly and kept standing up. I don't know if it was because I was pounding him or if he was just frozen, but he didn't move at all after that, and I was able to pound his face until his life bar was empty, all the way down from full. I must have activated the charge at the same time he was doing something in particular that messed him up, but I don't know what that would be.

With my slow gathering of energy (thanks to the locked camera) and no insta-Super Sonic, and a prettty standard second phase, from what I remember, I got a 2:16, so maybe there's a hint on the timing of the attack there. But since his attacks seem to be pure RNG, and I have no idea what I interrupted to freeze him, I doubt knowing the time helps. But this is something that happened, and I think it could lead to a much faster phase 1 if someone figured out what I did.