# Reflection phase shift and normal incidence

I have a rather basic question. Light that undergoes reflection also picks up a phase shift of $\pi$. Does it mean that light that is incident normally onto a perfect mirror simply undergoes perfect destructive interference with its own reflected wave?

This cannot be due to conservation of energy but I'm not sure how it can be resolved.

The total phase shift is $\pi$ at that point, but at other points there is a path length difference that contributes an extra phase shift $\Delta\Phi=-{2\pi\Delta x\over\lambda}$. This gives constructive and destructive interference in different locations.
Also, as an aside, the phase shift is only $\pi$ when the wave is reflects off a medium of higher refractive index than the medium it is traveling through. Otherwise it's zero.