While Telegram has a phone number-based authentication system, you can easily use the app without sharing any of your contacts. Telegram will still let you add users, and others can find you using your username.
By default, Telegram syncs your contacts to its servers. When a new contact joins, you get a notification about it. Your contact will also come to know that you're using Telegram.
If you want to keep your identity private, you can stop the Contact Sync feature. Telegram will still continue to work as it normally does. You can add users using their username, or you can create a separate contact in the Telegram app.
Here's how it works on the Telegram app for Android and iPhone.
Stop Contact Sharing in Telegram on Android
You can stop contact syncing in Telegram for Android from the Settings menu. To get started, open the Telegram app on your Android smartphone and tap the three-line menu icon from the top-left corner.
Here, choose the "Settings" option.
Go to the "Privacy and Security" option.
Tap the toggle next to the "Sync Contacts" option.
Now, Telegram will stop syncing new contacts, but the contacts that are already synced will still be available in the Telegram app.
To delete app synced contacts, tap the "Delete Synced Contacts" button.
From the pop-up message, select the "Delete" button to confirm.
Telegram has now deleted all contacts from your in-app contact book. When you go to the "Contacts" section, you'll find it empty.
Stop Contact Sharing in Telegram on iPhone
The process of disabling contact sync is slightly different in the Telegram app for iPhone.
Open the Telegram app on your iPhone and go to the "Settings" tab.
Navigate to the "Privacy and Security" section.
Scroll down and choose the "Data Settings" option.
Toggle on the "Sync Contacts" option to disable the contact sync feature.
Telegram will now stop uploading your local contact book with its servers.
To delete all synced contacts, tap the "Delete Synced Contacts" option.
From the pop-up message, select the "Delete" button to confirm.
Now, when you go to the "Contacts" tab in Telegram, you'll find that it's empty.
Did you know that Telegram doesn't have end-to-end encryption turned on for all chats? For that, you'll need to start a Secret Chat separately.