Fediverse

The latter doesn't try to establish you're an actual person though. This is something often also done by pro video games, to make bans hit more because they bam the phone number.

And spoofing won't work as you need to be able to receive texts on that number.

That's kinda the point, in virtually all countries phone number is way more directly tied to your IRL identity as a person than an email address would be. Hence its a pretty reasonable compromise to filter out bot operators as to them, using so many phone numbers is doable but a hassle, and they just move on.