Here are the steps to find a person on facebook with phone number.

1. Open your facebook account
2. Go to the search bar
3. Enter the mobile number and tap the search option
4. This search will give you the account synced with the number

This is how you can find a person on Facebook with the help of a phone number as all the accounts suggested are categorized by the phone number present on your device.

Source: https://getassist.net/how-to-find-someone-on-facebook/