From what I've seen, I couldn't find any accomplices either. This means one of three things (if we assume, as you rightly put it: an assumption, that Erik is not an extra scum outside the Phan, but part of the Phan or an NPC):
1 - Christine is at his side (unlikely, as this is only at the end of the story, and we're now around halfway through the story at the Maskerade)
2 - the Phan are people who have been invented for the sake of this game, i.e. were not in the novel, the play, the movie, at all.
3 - the Phan is made up of people who have a normal role in the Phantom, but have switched allegiances for the sake of the game. This is the mot likely scenario.

Still, a good shot at catching Phan is to find out who is and who is not part of the original cast of the Phantom. I already stated I was.
Of course, any Phans who are not from the Phantom will likely claim otherwise, and we'll only catch them with a name claim, but that's for later.