Worshipper – “Conquest” [Campaign 2, Mission 3]

How, HOW do you manage to defeat the elementals "without losses"? I have Phantom, and I reach them quite successfully, but then... everything gets destroyed, I just don't have enough damage. Please, describe step by step which elementals you're fighting, your army, the path to them, and the battle with them, if it's not too much trouble. Please =)

This mission is driving me crazy; I completed it on Veteran difficulty a long time ago, and now I can't seem to do it.