Telegram's policy empowers users with significant control over who can see their phone number. These settings are found under Settings > Privacy and Security > Phone Number.
"Who can see my phone number?": This dictates whether your number is displayed on your Telegram profile.
Nobody: The most private setting. Your phone number is never visible on your profile to any other user.
My Contacts: Only users you have mutually added as contacts (i.e., they are in your phone's address book and also on Telegram) can see your number.
Everybody: Your number is visible to anyone on Telegram who views your profile.
"Who can find me by my number?": This telegram number database controls if others can find your Telegram profile by typing your phone number into Telegram's search bar. This option becomes available if you select "Nobody" for "Who can see my phone number?".
Nobody: Prevents anyone from finding your profile via your phone number. You can only be found by your username.
My Contacts: Only people who have your number saved in their phone's address book and are on Telegram can find you this way.
Encryption at Rest and in Transit: Telegram states that all user data, including phone numbers and associated metadata, is stored "heavily encrypted" on its distributed cloud servers. Communication between clients and servers uses the custom MTProto protocol, ensuring encryption during transit.
Decryption Keys in Separate Data Centers: Telegram claims that encryption keys are stored in separate data centers in different jurisdictions from the actual encrypted data. This policy is designed to make it extremely difficult for any single entity (including governments) to access both the encrypted data and the means to decrypt it.
Contact Syncing (Optional): If you enable "Sync Contacts," your device's phone numbers (and associated names) are securely uploaded to Telegram's servers. This is used solely for contact discovery (to show you who among your existing contacts is on Telegram) and is not made public. You can disable syncing and delete previously synced contacts from Telegram's servers at any time.
4. Policy for Third-Party Interaction (Bots & API Clients).