How to change your phone number on Facebook, or remove it entirely
Facebook asks for a user’s phone number for a variety of reasons.
A phone number can be used to reset a forgotten password; to suggest people you may know so that you can connect with them on Facebook; and to keep the Facebook account safe with two-factor authentication and text alerts for potentially unauthorized logins.
You can easily change a phone number in Facebook through the platform’s “Settings” should you need to. Here’s how.
How to change phone number in Facebook
1. Log into Facebook on a PC or Mac, click on the arrow in the top-right corner of your home page, and select “Settings.”
2. Select “Mobile” on the left side.
3. If your account isn’t connected to a phone number, you can select “+ Add a Phone” to enter a number. If you’ve already entered a phone number, click “+ Add another mobile phone number” to add a new one.
4. Enter your number, and select if you’d like Facebook to confirm the number with a text message or with a call. Click “Continue.”
5. Enter the confirmation code you receive from Facebook and click “Confirm.”
6. You can remove a phone number on Facebook by clicking the “Remove” button below the number that you want to delete.
Source: BusinessInsider