There is no spoofing, so if the number is showing up is for sp1; it is likely that the calls are going out on sp1. Dialing from phone 2 doesn't mean the call is going out on sp2.
Go back to your dashboard and reconfigure the service on sp2. Check these two settings
"Make This Service the Primary Line to Call Out From" Phone 1 Phone 2
"Incoming Calls Will Ring On" Phone 1 Phone 2