I jump back and forth. After it drops a wave of block I return to the front layer then jump right back. It seems to make that phase go by a little quicker, but I could be wrong.

I guess I was just too terrible at that phase, haha. I solved it by getting a better rng where the boss did less bubble forms. Which isn't a real solution I guess, but it worked.

Also charge shot. Apparently.

You can use Solar Flare to destroy it's shield. It doesn't have to be fully charged.

Yeah, but when I posted this I didn't have the charge shot. I've now noticed later on that the boss doesn't really follow you into the corners, so I guess that's where you're supposed to go.

Maxed out power can push him away too... in case you haven't tried that.

If you're still at a low level and haven't obtained enough weapon upgrades or the solar flare, here's a way to avoid its bubble with the least amount of damage. The strategy is to plane shift right before it touches you. Then, when it launches the 'rain' attack (idk what it's called exactly) you quickly plane shift back and run under its bubble to the opposite side. There's a slight delay giving you enough time to run. After that, rinse and repeat as its bubble gets close to touching you again. It's a bit hard to avoid getting hit, but after a bit of practice it should be enough for you to kill the boss.

how do I use a charge shot? I'm starting to run out of chances to fight him, since I've now beat him 4 times.