This everybody knows since forever. Then the discussion goes towards Signal but Signal exposes the mobile number. Oh but get a burner number! Or use Wire! Or hey Riot.im!

But anyway that's not the aim. Your phone number is masked on Telegram channels, and even if the communication is not encrypted (it's only encrypted in secret chats), the aim is not to hide anything from authorities. If you want to do that, using a mobile is a flawed method, as a state actor will have the means to intercept different data and/or metadata. We can discuss at length the technical aspect of this, but the channel is a public channel so there's nothing hidden from the government.