A Monte Carlo model of a polychromatic laboratory based (coded aperture) edge illumination x-ray phase contrast imaging system has been developed and validated against experimental data. The ability for the simulation framework to be used to model two-dimensional images is also shown. The Monte Carlo model has been developed using the McXtrace engine and is polychromatic, i.e., results are obtained through the use of the full x-ray spectrum rather than an effective energy. This type of simulation can in future be used to model imaging of objects with complex geometry, for system prototyping, as well as providing a first step towards the development of a simulation for modelling dose delivery as a part of translating the imaging technique for use in clinical environments.