It requires a phone number, but it doesn't require sharing the phone number with other people. On signal you are only reachable via the phone number, Telegram has User names and allows to hide the number from the profile.
It asks for a phone number when you sign up, but you don't have to share the phone number with people you want to add as a contact/share it in groups.
For a lot of people, Telegram does a good job of being "less evil than Facebook Messenger", and private in ways that matter to them. I'm more worried about some nutcase from a video game meetup group getting hold of my phone number than I am law enforcement finding out I was in that video game group in the first place.
I have a Matrix server and an XMPP server for 'truly private' communication anyway.
