OK, I think I FINALLY figured it out, here's how you get to keep the firewall on and use the phone.
Log into your Obi device and in the set up wizard find your proxy server port (Service provider -> SIP). In your Motorola router, under Advanced/Port trigger, enter that port number in all 4 boxes and don't forget to select Enable, reboot your router and you should be good to go.
Under Advanced/Options/NAT ALG Status, I did uncheck SIP, not sure if that made a difference but after rebooting it as many times as I did I don't want to mess with it any more.