Power factor is the cosine factor of the voltage & current
phase difference. Its a short defination. But if you go
deeply, Power factor=cos@,its depend only on load, instead
of phasewise.if you connect same load in every phase it
will show same power factor value in each phase.Because
power factor is depended upon load resistance=R & its
cos@ = R/Z,
So if you are going to calcualte the power factor of all
phase, you have to calculate all resistance & impedance of
the load. Then you can calulate the avg. power factor.
Hope my answer will satisfy you.