This document describes techniques and apparatuses for implementing a phase control backlight. A phase control backlight is configured to concentrate light to each pupil of a viewer of a display to cause images to be displayed to each pupil of the viewer. The phase control backlight can include an illuminator and a light guide that includes a diffraction grating. The light guide is configured to receive light rays from the illuminator, and to diffract light rays out of the light guide via the diffraction grating. In accordance with various embodiments, the light guide can be controlled to alter a phase of the light rays as the light rays are guided within the light guide to cause the diffracted light rays to converge to a concentration point that corresponds to a position in space of each pupil of the viewer.