A Y-branch phase modulator made of an electro-optic(EO) polymer has been designed and fabricated. An EO polymer, PMMA-DR1, is used for the core layer, and UV-curable polymers, UV-15 and UV-15 LV, for the cladding layer. The rib type polymeric waveguides are fabricated by the reactive ion etching method and their EO effect is obtained by the poling process. The optical properties of the fabricated phase modulator are as follows: the halfwave voltage, $V_π$, is 25 V, the insertion loss of TM mode is -13.8 dB, and the intensity modulation is 0.17 % ($±V_π$).