I've had the same experience with Twitter: immediately after I sign up a new account (e. g. for a project or something) it get blocked for “suspicious activity”, and I get a prompt to verify a phone number to unblock it.
The same thing happened when I signed up for Twitter a few years ago. I emailed Twitter support and explained that I didn’t want to give them my phone number for privacy reasons, and they unblocked me. Never had a problem with it again.
I think there was an actual person on the other end of the ticket, I don’t think the odds would be very good if someone tried it nowadays.
