Answer
The reflection phase shift for ray $r_4$ is $~~0$
Work Step by Step
On page 1072, the text states, "If the light incident at an interface between media with different indexes of refraction is in the medium with the smaller index of refraction, the reflection causes a phase change of $\pi$ rad, or half a wavelength, in the reflected wave. Otherwise, there is no phase change due to the reflection."
Since ray $r_4$ reflects while it is in the medium with a larger index of refraction, there is no phase shift.
The reflection phase shift for ray $r_4$ is $~~0$
