I'm not sure I'll blame Twitter for (effectively) requiring phone numbers - they are stuck between a rock and a hard place.
On one side, people rightfully complain about trolls, harassers, spam, CSAM, misinformation campaigns and propaganda on online services. And on the other side, people will also rightfully complain about data harvesting, and an ever growing lack of anonymity on the Internet.
At the moment, phone numbers are the closest thing we have to at least have some cost associated with spamming and a legal pointer to get hold of criminal-level abusers. Using government IDs such as the German Personalausweis (which can communicate with a website using NFC and a special app) would outright kill anonymity, using middle men to do the same (or video/postal identification) like for banks, porn and gambling sites costs money and is not much better in terms of anonymity.
I want to be able to read the New York Times without a subscription too, yet here we are. Corporations don't have to give all their services to us for free. They can charge, require free registration, whatever.
You can request phone numbers when creating a certain number of tweets, or trying to reply to a well known account, or if upvoting a comment that is controversial or reported as spam.
It's a lazy solution that pushes spam control costs onto the users.
On one side, people rightfully complain about trolls, harassers, spam, CSAM, misinformation campaigns and propaganda on online services. And on the other side, people will also rightfully complain about data harvesting, and an ever growing lack of anonymity on the Internet.
At the moment, phone numbers are the closest thing we have to at least have some cost associated with spamming and a legal pointer to get hold of criminal-level abusers. Using government IDs such as the German Personalausweis (which can communicate with a website using NFC and a special app) would outright kill anonymity, using middle men to do the same (or video/postal identification) like for banks, porn and gambling sites costs money and is not much better in terms of anonymity.