Just a WAG: A lot of big companies have a “lock-box” for the remittance address. That is, a “clearinghouse bank”–and agent who starts the transfer of money from your account to the billing company’s account as soon as they get your payment. For the billing company, they get the money a lot sooner. Probably, based on your address, they might have decided that the Phoenix “lock-box” (whatever the “real” name is) is the most expedient one for them to receive their money as soon as possible.
(I’m not a banking expert. This is information I have gleaned being peripherally involved in this sort of thing, though.)