  On the mass neutrino phase calculations along both the particle geodesic line
and the photon null line, there exists a double counting error--factor of 2
when comparing the geodesic phase with the null phase. For the mass neutrino
propagation in the flat spacetime, we study the neutrino interference phase
calculation in the Minkowski diagram and find that the double counting effect
originates from despising the velocity difference between two mass neutrinos.
Moreover, we compare the phase calculations among the same energy description,
the same momentum description and same velocity description by means of the
Minkowski diagram, and obtain the practical equivalence of these three
descriptions. Further, in the curved spacetime, we also prove the existence of
the double counting of the geodesic phase to the null phase.
