A silicon-based electro-optic phase modulator includes a substrate, and an optical waveguide layer and an electrode layer that are stacked on the substrate. The optical waveguide layer includes a first doped region, and a first PN junction and a second PN junction that are connected in series. The electrode layer includes a first electrode, a second electrode, and a third electrode. The first PN junction is of a convex structure. One end of the first PN junction is connected to the first doped region, and the other end is connected to the second PN junction. The first doped region is connected to the first electrode. An end that is of the second PN junction and that is away from the first PN junction is connected to the second electrode, and an end that is close to the first PN junction is connected to the third electrode.