CMAttitude should report the "attitude" of the phone in terms of its orientation in respect of the earth, as stated by the docs:
An instance of the CMAttitude class represents a measurement of the device’s attitude at a point in time. "Attitude” refers to the orientation of a body relative to a given frame of reference.
So IF the compass bearing of Core Location's CLHeading does not help then you should be able to say which way the device is pointing (forward vs backwards) have a look at my question and answer here.