Where did you get this config from?
The phone is loaded with 9.X firmware, therefore the proxy settings should be using "USECALLMAMANGER".
Where is the config for the NAT (or not)?
When the phone is registering, look at the status messages. I bet the phone is complaining that the SEPmacaddress.cnf.xml file has invalid lines.
Search this forum, I've posted working configuration for the 9951/9971 and with little modification the same configuration can be used by the 7975.