A camshaft phaser includes a stator having a plurality of lobes; a rotor coaxially disposed within the stator and having a plurality of vanes interspersed with the lobes defining advance chambers and retard chambers; a camshaft phaser attachment bolt for attaching the camshaft phaser to a camshaft, the camshaft phaser attachment bolt defining a valve bore that is coaxial with the stator. A supply passage extends radially outward from the valve bore and includes a downstream end that is proximal to the valve bore and an upstream end that is distal from the valve bore and separated from the downstream end by a check valve seat. A check valve member in the supply passage is biased toward the check valve seat by centrifugal force. A valve spool is moveable within the valve bore such that the valve spool directs oil that has passed through the supply passage.