A camshaft phaser is provided for controllably varying the phaser relationship between a crankshaft and a camshaft in an internal combustion engine which includes a camshaft bearing for supporting the camshaft and which defines a mounting bore for mounting the camshaft phaser to the internal combustion engine. The camshaft phaser includes a housing with a gear drive unit disposed within the housing. The gear drive unit includes an input gear member and an output gear member such that the input gear member is attachable to the crankshaft and such that the input gear member is attached to an output shaft of an electric motor. The output gear member is attachable to the camshaft such that rotation of the input gear member by the electric motor causes relative rotation between the crankshaft and the camshaft. The camshaft phaser is disposed between the mounting bore and the camshaft bearing.