First think to know, you can only provision Obi302 from a Google Workspace admin account where you have added Google Voice standard or premier as a subscribed package (not starter). There you will be able to select the desk phone option and add the MAC address of the Obi302 to get it assigned to a user that has a phone number assigned.
I have Obi100 and Obi202 boxes which I historically provisioned via Obitalk and then added Google Voice to them that way. This does not work for Obi302, so please save yourself the headache of trying. I did out of habit and then eventually after no success, reached out to tech support for Polycom who informed me of the error of my ways.
After their redirect, I was able to get the Obi302 connected via Google Workspace in under 30 minutes. Figured I would post here since I didn't find any other guidance of this sort in my investigations for a solution.