We report on the construction of a lensless camera with a phase-modulating mask layer integrated directly on an image sensor using the UV-imprint lithography method. By replicating the master phase mask's surface structure directly on the image sensor, our method further simplifies the fabrication of lensless cameras and delivers a rigid and durable device with a small form factor. Our prototype device has an open-faced design without any apertures and generates high-quality photographic reconstructions with high light collection efficiency. We analyze the performance of our prototype device and demonstrate various imaging applications, including the digital refocusing capabilities.