On the surface that is true, but most folks understand it doesn't really work that way and facebook isn't really used that way. At a minimum, facebook is generally full of actual friends (for me, maybe 5 folks now), family (my family is large) and folks you generally have met from school and work and other folks you might know in a professional manner or through groups and activities.

Not all of these groups would have my phone number, but facebook isn't exactly a telephone service at its core.