They don't ask for a phone number until you post something that alerts the Ministry of Truth. Then your home page and any page you try to visit is replaced with a form to verify who you are.

I have four accounts that have been soft-locked this way. The whole point in my use is I do not want an identity tied to them.

But the user is not interested in posting (or they would have an account already). They are only creating an account because twitter is making them.

Twitter doesn't seem to have an option of a read-only account, where a phone number is only required to post.