If someone finds me by username, messages and I reply — will they know my number?
No. Replying to someone who found you by username does not reveal your phone number. The username exists precisely so that people can reach you without it.
What the other person actually sees
- Your display name, and your profile photo if your settings allow it.
- Your username.
- Your bio, if you wrote one.
- Your last seen time, according to your privacy setting.
The phone number is not in that list, and no amount of conversation adds it.
The one exception
If the person already has your number saved in their contacts, Telegram will show them that this account belongs to that contact. It is not revealing anything new: they had the number before the conversation started. Nothing you do inside the chat causes a number to be disclosed.
Check and set your own rule
- Open Settings, Privacy and Security, Phone Number.
- Who can see my phone number controls who sees the number on your profile. Set it to Nobody if you want it hidden from everyone.
- Who can find me by my number controls whether someone holding your number can locate the account at all.
When "Who can see my phone number" is set to Nobody, Telegram offers an exceptions list so that chosen contacts can still see it. That is usually a better answer than leaving it visible to everyone.