Phone number is also good because you can be reasonably sure as to whether it's voip or not. It is literally the one non-awful solution to the sybil problem we have discovered (the awful ones being things like gov id).
There's no way in he'll I'm going to create an account on every site I want to read, and absolutely I'm not submitting my number for the eternal, unrelenting spam.
I have enough crap from the legitimate companies selling/leaking my number, to now deal with _that_.
