TThe electrooptic effect for most materials is very small, on the order of 10^ -12 [V/m]. It can be significant if the electric field is applied at close range to the electrodes. The effect on phase can be significant if the electric field is applied over a long distance of propagation. This is the reason OptiBPM expects the electric field will be made by electrodes in the transverse plane, and will follow the propagation so that the eo effect can accumulate as it propagates. OptiBPM follows these design rules. OptiBPM can usually simulate most EO phase modulators that follow the above design rules.
The attached sketch shows application of the electrostatic field over the length of propagation, but the electrodes are as far apart as the length of propagation. The resulting electric field and EO effect will be preduced. I fear the modulation of the phase will be so small it cannot be measured.