Can confirm this. Tried to set up a new Twitter account for business use, got the phone number challenge but wasn't able to go any further because the number I wanted to use was "already in use" i.e. my own number I already stupidly associated with my personal twitter account.

To add insult to injury I've been suspended permanently because Twitter's "offence" AI can't distinguish between black humour and a direct physical threat. But that's another story.