A phase modulation module and an electro-optic modulator are provided. The phase modulation module has an input end face and an output end face and comprises a substrate, an isolation layer, a waveguide layer, and an electrode layer which are arranged in sequence. The electrode layer includes a plurality of electrodes which are arranged at intervals and configured to form a modulating electric field region. The waveguide layer comprises a plate layer, a first ridge layer and a second ridge layer which are arranged in sequence in a direction away from the substrate, wherein the plate layer extends to the input end face and the output end face; the first ridge layer protrudes in a ridge shape from a surface of the plate layer, extends to the input end face and the output end face, and is partially located in the modulating electric field region; the second ridge layer protrudes in a ridge shape from a surface of the first ridge layer, has a spacing from each of the input end face and the output end face, and is partially located in the modulating electric field region; and the second ridge layer and the first ridge layer form at least one waveguide arm extending to the input end face and the output end face and modulated by the modulating electric field region.