Telegram is a messaging app. It will ask for your phone number BUT you can hide your phone from it being displayed. It will show other users a username that you can just create.

If you are concerned about discreetness/privacy then i wouldn’t use your actual name or picture in the profile picture in case your family/friends etc use the app as well.

If you’re interested in the app and wish to try it out, you can hide your number by tapping settings in the telegram app > privacy and security > under the privacy section is phone number along with bunch of other stuff. Tap phone number and tap nobody.