Even in your case, there are some possible ways for Facebook to know your number. People on your "friends" list may have allowed Facebook to sync their contacts

Even in your case, there are some possible ways for Facebook to know your number. People on your "friends" list may have allowed Facebook to sync their contacts (and allowed continuous sync) from their address books on email accounts or with the Facebook app on their devices. Especially if any of them are or were using a version of Android older than Marshmallow (6.x), where app permissions are/were granted at installation time on an "grant all or can't-use-the-app" basis, here are the permissions they have definitely granted the Facebook application [1]: * Contacts find accounts on the device read your contacts modify your contacts * Phone directly call phone numbers read call log read phone status and identity write call log Even if different people in your address book use slightly different names to refer to you in their address books, it wouldn't take a lot for Facebook to figure out what your number is. And just because Facebook asks you for your number, it does not mean it isn't using information obtained from others. [1]: https://play.google.com/store/apps/details?id=com.facebook.katana https://play.google.com/store/apps/details?id=com.facebook.k... (Check the Permissions section at the bottom of the app page and click on "View details" to see the list of permissions it asks for.)