How does FB know my phone number?

Question

I have never shared my phone number with FB, not even for the 2FA purpose. I use a FB app on my Android phone, but it also never requested a permission to use my phone number. When I checked on FB before the leak there was no phone number in my account information. Yet my phone number, along with all my other credentials, is in the recent leak. What am I missing?

aritmo · Accepted Answer

The weakest link is some of your contacts that opted (because that is the default) to upload their phone contacts to a Facebook service. Through those phone contacts, Facebook correlates the contact name with your Facebook account.

TheRealSteel · Answer

Someone you know signed into WhatsApp, which uploads all your contacts to Facebook without their permission.

johnx123-up · Answer

I may be wrong. But, based on this solution https://stackoverflow.com/questions/58128546/how-to-get-the-... permission is not required to get phone number--if we use play services API

cyberlab · Answer

Maybe I'm wrong, but I imagine if you use the Facebook app on your phone, then Facebook can grab your number and attach it as metadata in your account.

foobarbaz33 · Answer

Did you not read the small print when you agreed to become a human centipede?