For the first phase, spam him with missiles or regular beam shots as much as you can and don't let yourself get cornered against walls by his 3-strikes melee attack, spin jump above and behind him to get free when he does it.
He'll sometimes shoot a laser up in the sky, get close to him before the laser comes back down in a massive attack that strikes everywhere but near him.
He'll sometimes do another beam attack that strikes everywhere except low to the ground, so duck and prepare for a melee counter he does right after that.
When he charges up his gun and releases a big glowy purple energy ball, charge up your Power Bomb and detonate it to break the big purple ball to get some get health and ammo.
Whenever he tries to melee you and you get a counter "click" noise, try your best to counter it and that's your cue to spam missiles during the cutscene.
After the first time you block him, he gets armor that prevents all damage but he'll use his melee attack and you can block him again to end Phase 1.
Depending on how much damage you did prior to the block cutscene, you'll get to spam missiles right up until he switches to phase 2, or you'll have to do some more of the phase 1 strategy until you block him again.
In phase 2, he grows wings and flies above you in the room. He gets several new attacks.
He'll fly low and into a wall, it does pretty significant damage unless you slide under him but he's quick so it takes some getting used to.
He'll fly above you and crash down vertically, phase shift away from him and blast him.
He'll hover around the room and charge up his gun, leading to two possible attacks : a huge diagonal blast, that's a good chance for you to spam him with missiles or beam shots. Or a gatling type of beam spam that'll circle around the room, so just spin jump up and around the boss, he'll sometimes do a couple full circles so don't stop too early.
Once you damage him enough, you'll get into Phase 3 where he's back on the ground.
In Phase 3, he'll have his usual attacks from Phase 1 but also sometimes release a huge sun-like ball that'll constantly send damage waves until destroyed, so again use your Power Bomb as soon as you see it, and you'll get some ammo and health.
He's a bit quicker than Phase 1 I felt, but the attacks are mostly the same, damage him until you get a cutscene for another TWO counters in a row (he'll raise his hand as if to bitchslap Samus in the first block).
If you spam him enough, the fight ends there and you'lll get a cinematic. After the cinematic, you'll have another short interactive cutscene where you just need to power up and spam your new beam attack against the new form of the boss and then you have to escape from the planet before it goes boom. The escape isn't as straightforward as Super Metroid, but remember to spam your new beam attack everywhere to destroy walls or other obstacles that don't even look destructible in the first place, and make your way to your ship for the final cutscene.