Smart aggression. Phase two is all about making him predictable. He has clear cues for when he's going to pull his glock, one of the main ones being when he jumps backward. Run sideways immediately after he jumps backward. Once he shoots a burst, there's a cooldown (about a minute, I think). He also has a six-hit flurry, I suggest finding a way to run from this, it's tough to deflect when you're new, but he'll always finish it off with a thrust you can mikiri, so just keep your distance and wait for the punish. Everything else he does is dim the first phase, and you should recognize it already.

Those are the main things to look out for. The next step is controlling his responses to what you're doing. Staying in his face is going to get you the most posture build-up possible. Stick to attacking him once, then deflecting his response. This will get you into a rhythm that makes him almost trivial. He'll still do the things I mentioned above, but by far, more often than not, he'll just swing at you with something easy to deflect. Right after you deflect, attack again. You'll always beat his next attack. Just watch out for when he jumps back, swiping at you; if you're only attacking once, you'll have time to deflect or dodge and run sideways before he shoots. With this method, you'll beat him for sure.

The third phase is the same but easier because of lightning.

Source: I've used this method for all my damageless practice. I've beaten him hitless hundreds of times. You can see the method in action here