Start the level from the beginning; the level should start with Tartarus dropping you off on a ledge. An Enforcer gets behind you, but Tartarus drives it away. Continue playing until you get to the point where you drop down a piston tube and see no enemies, but evidence of a conflict. This area has multiple crates of weapons and bodies lying about. If you walk to the ledge facing out of the stage and look down, you should see a Phantom floating there, several levels below your current location.