You can add or remove a mobile phone number from your account in your settings. We recommend that you always add an email to your account to help you gain access to your account in case you ever lose access to your mobile phone.
To add your first or another mobile phone number:
In the bottom right of Facebook, tap menu.
Scroll down and tap Settings & privacy, then tap Settings.
In the Account section, tap Personal and account information, then tap Contact info.
Tap Add phone number, enter your number and tap Continue.
When you add a number, you may be asked to enter a confirmation code. If you don’t get a text message with a confirmation code, check to make sure you’ve turned on mobile texts.
Enter your confirmation code and tap Confirm.
To remove a mobile phone number:
In the bottom right of Facebook, tap menu.
Scroll down and tap Settings & privacy, then tap Settings.
In the Account section, tap Personal and account information, then tap Contact info.
Tap the phone number you’d like to remove, then tap Remove.
You can also tap the dropdown menu to change who can see your phone number (example: Only Me).
Enter your Facebook password, then tap Remove Phone to confirm.

or use your email