I do remember something between Coinbase and the IRS but I didn't pay attention because I am not in The U.S. It was something about the IRS asking to Coinbase to report some users with $xxxx traded and Coinbase was against it but I don't remember how it ended.
As for your problem with Gemini I would say never use a phone number like google voice, most websites don't accept such number, and even if you find one it can be a matter of time before they ban it, and it can bring you some problem later.
I haven't heard about Bitstamp reporting to the IRS but isn't BitPay allowing U.S. citizens as well?