How does Facebook use my mobile phone number I added for two-factor authentication?
When you add a new mobile phone number for two-factor authentication, we’ll use it to help you log in to Facebook and help keep your account safe. If someone tries to log in to your Facebook from an unrecognized device or browser, we’ll send you a text message alert and ask you for a verification code.
Keep in mind, mobile phone numbers added to other places on Facebook and Facebook Company Products (example: Marketplace, your Facebook profile) may be used for other purposes including suggesting friends or providing ads.
For security reasons, you won’t be able to use the same mobile phone number that you use for two-factor authentication to help you reset your password. You’ll need to have a different mobile phone number or email address added to your account to reset your password if you ever need to.