Light field microscopy, featuring with snapshot large-scale three-dimensional (3D) fluorescence imaging, has aroused great interests in various biological applications, especially for high-speed 3D calcium imaging. Traditional 3D deconvolution algorithms based on the beam propagation model facilitate high-resolution 3D reconstructions. However, such a high-precision model is not robust enough for the experimental data with different system errors such as optical aberrations and background fluorescence, which bring great periodic artifacts and reduce the image contrast. In order to solve this problem, here we propose a phase-space deconvolution method for light field microscopy, which fully exploits the smoothness prior in the phase-space domain. By modeling the imaging process in the phase-space domain, we convert the spatially-nonuniform point spread function (PSF) into a spatially-uniform one with a much smaller size. Experiments on various biological samples and resolution charts are demonstrated to verify the contrast enhancement with much fewer artifacts and 10-times less computational cost by our method without any hardware modifications required.