Facebook asked to "increase your privacy level"?

[the_happy_green_fish]

So the person in question added their mobile number. Her security settings are all private.

She began receiving calls from a random number, and them discovered that Facebook had put her number on her profile without asking. Does anyone know why this has happened? I'm having difficulty finding this online.

She accesses from a computer, not a mobile, so it's not going to be the smartphone issue. Thanks all.
I'm not asking how to increase the security levels. They are as high as they can go. She didn't add it to her profile, she gave the information to Facebook with the understanding that it would be used to increase security, not put on her profile.

I don't want to know how to delete it, that's already been done. I want to know why it happened in the first place.