Big Sur is a Major update for your Mac and by the time I’ve written this it will probably be there.
In my experience, I believe it is a wise move to remove your mobile number from your Facebook Account. Recently it was revealed that in some cases Facebook was tracking calls and text messages from mobiles.
You will also reduce the risk that someone pretending to be Facebook will trick you into giving them your private details—including your password. Also if your account gets hacked the hackers won’t be able to see your mobile number if it’s removed from your account.