I believe this is widely known as 'dark profiles' can't seem to find that many articles but here is one: http://www.dailymail.co.uk/sciencetech/article-2165543/Faceb...

Also they keep track of that info easily when somebody migrates their phone address book on to the Messenger or Facebook app, on first install it prompts you to push all that data. They have your name, number and the connection between that user and you.