A camshaft phaser includes an input member and an output member defining an advance chamber and a retard chamber; a valve body having a valve bore which extends along an axis, an annular groove extending radially outward from the valve bore and having a first width in the direction of the axis, and a passage which opens into the annular groove and which extends from the valve bore through the valve body radially outward from the valve bore such that the passage has a second width in the direction of the axis that is greater than the first width of the annular groove. The camshaft phaser also includes a valve spool which moves along the axis within said valve bore, the valve spool having a land which varies a flow area between the valve bore and the annular groove and between the valve bore and the passage.