This Letter introduces the design and simulation of a microstrip-line-based electro-optic (EO) polymer optical phase modulator (PM) that is further enhanced by the addition of photonic crystal (PhC) structures that are in close proximity to the optical core. The slow-wave PhC structure is designed for two different material configurations and placed in the modulator as a superstrate to the optical core; simulation results are depicted for both 1D and 2D PhC structures. The PM characteristics are