We present a software simulator for the modeling of astronomical instrumentation, which includes platform effects and software processing. It is an end-to-end simulator, from the entrance of the telescope to the data acquisition at the detector, along with software blocks dealing, e.g., with demodulation, inversion, and compression. Developed following the Solar Orbiter/Polarimetric and Helioseismic Imager (SO/PHI) instrument, it comprises elements such as a filtergraph, polarimetric modulator, detector, vibrations, and accumulations. Through these, the simulator performs most of the analyses that can be done with light in astronomy, such as differential photometry, spectroscopy, and polarimetry. The simulator is coded with high flexibility and ease of implementation of new effects and subsystems. Thus, it allows for the user to adapt it to a wide variety of instruments, even not exclusively solar ones, as illustrated with an example of application to a night-time observation. The simulator can provide support in the phase of instrument design and help assess tolerances and test solutions to underperformances arising during the instrument operations. All this makes SOPHISM a very valuable tool for all the stages of astronomical instrument definition, design, operation, and lifetime tracking evaluation.