Many years ago, Facebook started to ask for phone number for "security reasons" and so that you wouldn't "lose access to your account". They emphasized that the

Many years ago, Facebook started to ask for phone number for "security reasons" and so that you wouldn't "lose access to your account". They emphasized that the number wouldn't be used for anything else. I never gave it, and nowadays don't even have an account, and wasn't surprised when it was later revealed that they were lying.