Correct me if I'm wrong, but I don't think Epeiros' victory conditions extend into Gaul or Iberia. In which case, why would you need to be producing phalangites over there in the first place?

Aside from that, the Italo-Gallic border should be on the fringes of your empire. Conceptually, it's supposed to be far enough from your power base that you aren't going to have a firm grip on it, i.e. won't be able to call upon your best "homeland" units for frequent service there, because it's a pain to transport them over there in the first place. You have to rely on weaker local auxiliaries, a small amount of factional troops (e.g. Thureophoroi produced in Massilia), and mercenaries to secure the borders--not the elite of the elite.

That said, I'm sure there is a way to modify the game to eliminate this element, but I don't know how.

Cheers.