My bad, I put all the details into the question above:
Do I have to match the Portal version to our software version? We are running ArcMap 10.3.1 on a versioned, enterprise GDB. My goal was to install ArcGIS for Portal on a separate server for testing before deploying to the rest of the organization. Will the most updated version of Portal work with ArcMap 10.3.1 or do I also have to install a newer version of ArcMap or ArcGIS Pro?