ADVR, Inc. proposes the development of a fiber coupled, high power, electro-optically controlled, space qualified, phase modulator for the NASA Laser Interferometer Space Antenna (LISA). The proposed device will be capable of phase modulating a 1 W or greater, continuous wave optical signal at multi-gigahertz rates at 1064 nm. The key innovation is the use of a waveguide embedded in a non-linear optical material suitable for high optical power handling. The phase modulators used for LISA must be rugged and must perform optimally in a radiation environment over the mission lifetime. To achieve this goal, the proposed phase modulator development will include a fiber-in-fiber-out design that will readily lend itself to future space qualification for mechanical stability of the package and radiation damage resistance of the non-linear optical material.