When you use Facebook you have to prove that you are a bona fide person. This is commonly verified by using your mobile phone number and having a verification text sent to it.
If you’re unable to verify your identity using a mobile phone number, you can submit a request to verify your identity using your government-issued ID.
If you’re seeing an error message that your mobile number was recently used to verify another account, please try a different number or wait a few days before trying to verify your account with that number again.
Keep in mind that you can only use your mobile phone number to verify one account. In addition, if you signed up with your phone number and verified it, your account is already confirmed.