A cam phaser (10) dynamically adjusts a rotational relationship of a camshaft (24) of an internal combustion engine with respect to an engine crankshaft (34). A cam sprocket (20) can be driven by an endless loop power transmission member connected to a drive sprocket (36) mounted for rotation with the engine 5 crankshaft (34). The cam phaser (10) can include a planetary gear drive train (12) having a centrally located sun gear (14) connected for rotation with the cam sprocket (20), a ring gear (18) connected for rotation with the camshaft (24), and a plurality of planet gears (16a, 16b) supported by a carrier (22) in meshing engagement between the sun gear (14) and the ring gear (18). A phase adjustment gear (26) can be 10 connected for rotation with the carrier (22). The sun gear (14) can drive the planet gears (16a, 16b) in rotation thereby causing the ring gear (18) to be driven in rotation. Rotational movement the phase adjustment gear (26) can adjustably vary a cam phase position of the camshaft (24) relative to the crankshaft (34).