It takes as many (or more) conductors to accomplish 2 phase as it does 3 phase, and because you can get more net power from the same size conductors with 3 phase, people stopped using 2 phase very early on. The only places it still exists are small pockets of old legacy industrial users, such as some old furniture factories around Philadelphia, a few places in upstate New York and maybe one or two others where the industrial facilities were built around the turn of the last century, when electrical distribution was in its infancy. Since you can't buy new 2 phase motors, even those are more museums than production facilities in many cases. So very few electricians come across it in their careers and even then, usually in upgrading to 3 phase.
