Facebook has your data.  We all know it.  It's how it makes money on a free to use service.  As a user you reap all the benefits of being able to keep in touch with people, find old friends, share pictures of cats, watch videos of people falling over, and keep an eye on people you went to school with but haven't spoken to since year 9.  As a trade off, they use the information about you as a way to make money.   Its a two way street.  Much has been made of data on Facebook and privacy settings, but it seems here that Facebook can now find out information about you - namely here your phone number -  that you haven't given them. 

Now there will no doubt be cries of how utterly unacceptable that is - which actually, I don't disagree with.  However, given how well documented and reported the use of and access to data on Facebook has been, I don't find it surprising.  

If I really had a problem with Facebook accessing data about me, I wouldn't use it.   However, I do use Facebook - I love it.  For me, Facebook accessing information about me is part and parcel - if you don't want it to know about you, don't use it.