I had big trouble with this fight. Your best bet is moving constantly to the next add before the first one reaches 50% and trying to cleave them down at the same time with chain lightning, use SWG. If you get around 1 min 10 seconds left at the end of the first phase you'll be ok generally if you use all your cooldowns.
did it on the 2nd try (1st try I got to much damage from the smaller sparks). I watched a video on youtube to get an idea of the fight. in the end I had only ~53s when p2 started, used my pe fireelemental hero and ascendance and got it. I guess the better your gear is the more time you can "waste" in p1. I have ilvl 529 with 4pc, legendary meta and 2 tot trinkets.
p1 I fought against angel no 1 and when he was at 50% I moved byhind the paladin and had the luck to get the 2nd angel on my way. grabbed the third one after the 2nd was attacking the paldin again.
Phase 1 is the key to this fight. If you don't get into phase 2 with ~1min left on enrage, you won't be able to nuke him down in time.
As Nivena said, dps-ing multiple angels at the same time can make phase 1 much faster. RNG can also work in your favour/against you depending on where the "angel orbs" appear. If you're lucky they'll all be quite close together and you won't have to spend so much time running, but it's hard to rely on this being the case.
So yeh, try and get all 3 angels out ASAP, nuke them all down, and aim to start phase 2 with about 1 min to enrage. Save heroism and all your CDs for phase 2 as well.
also the four corners (at least on the horde side) are safe spots, so no stars will hit you there.
when the fight started I didn't dps him before he knelt down, I waited (so not to lose out on meta gem/trinket procs). I stood on top of him as soon as the angels spawned so to minimize the distance to the 1st angel.
I also heard that you could thunderstorm him to the side, with this you could avoid the collapsing stars in the middle...I think I read that on wowhead.com (google : Ahoo'ru wowhead). For my successful attempt I didn't thunderstorm him.