Yeah, I vaguely remember they said that was a thing. I still have probably about ten google accounts and none of them are tied to a real phone number.
It's been years since I set them all up, so I don't remember exactly how I got around that, but it seems like it wasn't terribly difficult. Maybe I used Skype?
They only do the real number check when you are first creating the account right before number selection. They never ask you again to confirm or do any kind of verification with the real number.
I've had to change my phone number a few times over the decade and my personal gvoice is verified with whatever number I had 10 years ago. I just don't set it as a callback or text receiver.
It's been years since I set them all up, so I don't remember exactly how I got around that, but it seems like it wasn't terribly difficult. Maybe I used Skype?