"about a minute" is the right amount of time for a SPA to look for a new configuration (ie, self provisioning). If your phone is doing that, it is possible that the auto-provisioned configuration is causing the phone to drop its connection. between power on, and provisioning, all it can go on is its DHCP values, plus its stored configuration from the last boot.

Try removing the phone-specific provisioning configuration, so it cant find it so can't load it. If it now stays accessible, you know there's something in the configuration causing a problem.