According to Symantec, Facebook android app has a bug which collects the phone number of the android user without permission. They have contacted Facebook about this bug and said that it was corrected with its updated android app which was updated on 27th June, 2013.
If you have not updated your Facebook android app, please update now, as it will correct this bug. Please visit Google play – Facebook to update your android app.
Amazon (E-Book): Facebook For Dummies (Carolyn Abram)