Blacklist: fix NPE

getCallerInfo() can be null if the caller info is being
asynchronously read. Use a different method to get the phone number.

Change-Id: I4b77552a3e3cddd6d3fc9ba8e13721d7431f6141
(cherry picked from commit 0343fed4f66c9765dbce525fb1e0906de2d5991f)