The conversion approach is noted at the very bottom of the PMSM component documentation, where KE is the peak-phase voltage, φM is the flux induced by the magnet, and p is the number of pole pairs.

KE = φM·p

Note that if your BEMF constant is line-to-line, opposed to the phase voltage, then you will have to add another scaling factor of sqrt(3) for sinusoidal BEMF.