  We theoretically study the phase of the reflection amplitude of an electron
(massive Dirac fermion) at a lateral potential step in Bernal-stacked bilayer
graphene. The phase shows anomalous jump of $\pi$, as the electron incidence
angle (relative to the normal direction to the step) varies to pass $\pm
\pi/4$. The jump is attributed to the Berry phase associated with the
pseudospin-1/2 of the electron. This Berry-phase effect is robust against the
band gap opening due to the external electric gates generating the step. We
propose an interferometry setup in which collimated waves can be generated and
tuned. By using the setup, one can identify both the $\pi$ jump and the
collimation angle.
