Telegram will soon release an update that will allow users to completely hide their phone number. Even from those who entered it in the contact list.
The reason for the introduction of such an option was riots in Hong Kong. Activists suggested that authorities could find a way to find out the personal data of the protesters. For example, add a common base of numbers to the contact list, and then track which of them will appear in the protest chats. Thus, it is not difficult for the police to find out the identities of users.
Now users of the Messenger can hide their number, but not from everyone. If someone saves it, then regardless of the privacy settings, the number will be displayed in Telegram.