If you give someone your phone number, they will probably store it somewhere. In the olden days that used to be in a paper address book. A decade or two ago it might have been an electronic address book on a desktop computer, perhaps as part of email software. Think Outlook. Nowadays, people use more than one "device" (home computer, work computer, phone, perhaps they have both a desktop and tablet PC at home, etc.) and want to access their information (including your phone number) from all of them, and so store that information in the cloud. I don't understand why that comes as such a shock to people who are, presumably (since they read El Reg), reasonably tech savvy.
Equally Facebook does not pull your phone data without your permission. Nobody will get to see your phone number on Facebook except for those people you've already shared it with. If you put your phone number on Facebook and share it with your friends, then it's no surprise that it appears in their Facebook contacts list (which has been a feature of the site for many years now) - and not only is it no surprise, it's no big deal. You put your phone number on Facebook, you make it available to all your friends, you make someone your Facebook friend, they can see your phone number. That is not new, shocking or surprising in any way.