UA and AA both allow international upgrades to clear up to time of departure and I have never heard of phantom premium class bookings being an issue at either airline. The systems there seem to work just fine - higher status and fares improve your chances of clearing, but no seat goes out empty as long as someone with the means to "pay" for the upgrade (money, miles, SWUs) is willing to buck up for it.

Two serious questions:
Is there something unique about CO that attracts Phantoms? Other airlines I fly don't seem to have this problem.

CO has among, if not THE, best customer web sites and their other IT stuff seems top-class as well. Surely it wouldn't be that hard to program a solution to the phantom bookings, if they indeed exist?

Personally I think the whole thing's a red herring...