Is the light is propagating along the positive $z$-axis and its is reflected from plane then correct phase for reflected light is $\mathrm{kx}-\mathrm{kz}-\omega \mathrm{t}$ and for electric field as the light incident on Brewster angle so the reflected light should be perfectly plane polarized that's why polarization direction should be $y$-axis so electric field of reflected light contain no z-component.