

OpenAI allows you to signup with your Google Account. Last Time I checked there was no requirement to provide a phone number for that. But even if, what the hell is so special about your phone? If you still use MFA over Text, you shouldn’t be worried about some random company having your phone number, but rather about why you use the weakest form of MFA in the first place.
Also, just by someone knowing your phone number, you don’t compromise your phone number. If that’s the case, better get a new one and make sure none of the people you ever give it to use Whatsapp or anything of that sort or your number will be in someone’s database at some point. Don’t ever call anyone with that number as they will have acces to it afterwards (and no, just disabling Caller ID doesn’t necessarily work to prevent this).
I’m not sure what kind of paranoia you’re suffering from, but dude, touch some grass. Nothing of what you said makes any technical sense.
No.