Yes, firmware management has always been completely FUBAR, and nobody here has a definitive firmware version list, nor have release notes been published in years.
When I posted my previous reply, I was basing it on a 1022 that is only running Callcentric. I just now plugged in my 1032, which is running CC and three Google Voice numbers. Its firmware is 5.1.11 (Build: 4858EX.1311)
When you removed your phone from the OBiTALK portal, did you also restore the phone to factory defaults (two methods: key in ***8 then 1#, or by holding down the Home and Back keys and then powering it on per
https://www.obitalk.com/info/faq/obi-ip-phone/phn-factory-reset ).
If you did not do that specific task, then I suggest removing the device from your OBiTALK portal, wait about 5 minutes, then restore it to factory defaults, and then re-add it to the portal. Don't make any custom configuration changes. Wait until it finishes rebooting (probably more than once), then add a Google Voice number, wait some more, until it says "Connected" status, and finally, check the FW build again.