Answer
The variable $h$ in the equation $y = \cos (x - h)$ determines the horizontal (phase) shift of the graph.
$y = \cos (x - 0)$ -> no phase shift
$y = \cos (x - \frac{\pi}{6})$ -> $\frac{\pi}{6}$ or $30^{\circ}$ phase shift to the right
$y = \cos (x - (-\frac{\pi}{6}))$ -> $\frac{\pi}{6}$ or $30^{\circ}$ phase shift to the left
Work Step by Step
See below graph for reference: