If you have the Facebook app on your iPhone, you've agreed to allow Facebook access to all your phone's contacts. If you don't remember giving that permission, neither do I; but apparently, it's part and parcel of the terms of service. Don't worry, though; there's an easy way to change this sharing setting and make the names and numbers in your Contacts app private again. Let's get started learning how to stop Facebook from accessing your Contacts on iPhone.