People have long complained that Signal violated their privacy by requiring them to hand out phone numbers. With someone's phone number you can discover everything about them, even location - it's possibly the most valuable ID.
For example, imagine you are a young female giving contact information to someone on a temporary basis; you might not want to hand out your phone number everywhere.
Especially when signal can't even make phone calls or text messages, there's no need for it to know my phone number
It can...
It can't. Signal calls are over the internet, not the PSTN. And Signal removed SMS support last year.
just use a landline from some phone booth, done. You only need it to create the account, never again after that.