Proper positioning of Charge greatly aids ranged in killing ghosts because they're quite fast if they get out of it and can't all be killed if they are not slowed in most cases.

You need to always lay charge in a line directly from the stack to the white portal, and everyone needs to stay stacked by the boss, on top of the red portal, to kill the Dominators as quick as possible when they spawn. Also, if people start moving around at all they they're going to scatter, which means ghosts will go everywhere and get out of control.

The ghosts do shit tons of damage to the construct as well if they explode near it, which will dump you back into Phase 1, so it isn't just the ranged stack you're protecting. You do not want ghosts getting anywhere near you, but they will if you do not keep all of them in the slow.

When my group does this, the Construct focuses on the boss and only diverts to lay charge two times, and prison ghosts once when the boss is < 10%. So, lay down your first charge, hit the boss, lay down a second charge beside it for a bit more coverage when it comes off CD, and then back to the boss. We designate our two or three top ranged DD (ideally Hunters) to deal with ghosts when they're out.

At the end, when the boss is very low, drop a prison in front of the white portal so that everyone can tunnel the boss.

If the fight drags on because of low DPS, then you may have the portals swap and you'll have to lay down charge again. Other than that, you should be on the boss full time. I just use Reverberating Blow and Fel Orb on the boss on CD. There may be some better use for the Orb, but if so I haven't found it. We have ranged interrupt the caster spawns so they will walk over to the stack, and then just cleave them down without giving them much attention.

The rest of the time you should be straight out meleeing the boss.

RB is a frontal cone, so it should hit the Dominator and the boss both if they are together in front of you at the red portal, as they should be. However, the stacks only boost damage from subsequent RB hits, so it may or may not add up to much additional damage depending how fast the Dominator dies. It will, however, continue to stack on the boss, so it makes a difference on him.

(By the way, you need to right click on the boss to make the Construct auto-attack if you did not know to do that. It took me a couple times in this fight to figure that out, but maybe that's just me.)