Hi Carl:
Google Voice is an inbound call forwarding service. By design, people call your Google Voice phone number, and then it forwards that call (rings to) any combination of up to six forwarding phone numbers, optionally including a authorized OBi device.
You need to actually have an inbound Google Voice phone number, to be able to receive calls on your OBi. Right now, you don't have a Google Voice phone number, so nobody can call you. OBi devices are making outbound calls via Google's Chat system. When you don't have your own GV phone number, it substitutes a generic Google caller ID for all calls, made by everyone. Nobody can call that number to reach you. It's just a dummy caller ID.
You need to get a Google Voice number. Either select one from Google's pool of available numbers, or else you can port in a mobile phone number, and thus turn that into a Google Voice number.
For more information, you can read the Google Voice help pages, starting here:
https://support.google.com/voice/#topic=1707989