A phase grating image-sensing device. The device includes a plurality of photodiodes, a smoothing layer, a color filter layer and a plurality of phase gratings. The photodiodes are formed on a substrate and isolated from each other by isolation structures. The smoothing layer covers the photodiodes and the isolation structures. The color filter layer is embedded within the smoothing layer forming a sandwich structure with the smoothing layer. The phase gratings are formed over the smoothing layer positioned at corresponding locations above isolation structures. The phase grating layers produce a constructive interference of light passing through the smoothing layer.