Gizmodo ran a piece a couple of days ago suggesting that Facebook uses the phone number you provide for two-factor authentication in order to target you with ads.
And it turns out, this is true. Facebook uses the information you provide such as your phone number, potentially even security questions, as additional ways to gather information about you. The phone number is then used to link you to contact lists imported by other users and over which you have no control. The data in other people’s contact lists is then incorporated into the dossier that Facebook compiles on you, presumably including all email addresses you may have ever used.
Facebook cannot be trusted with any personal information. That’s why I deleted all of my posts, likes, comments, shares, photos and videos posted since the beginning and no longer post on FB. Facebook continues to operate in a reckless and dangerous manner is literally begging for government regulation.