The only resolution that I was able to come up with was to have Autodesk remove the parameter from my files, which, I think, requires a subscription.
As to the cause, at least in my case, the GUID for the "Phase" parameter from the family files in question matches the GUID for the parameter "Phase" that I used from the "Revit_Master_Shared_Parameters.txt" file that I downloaded from Autodesk Seek. However the parameter from the manufacturers' families is an Integer type, while the one from Autodesk is a "Number of Poles" type. This seems be what leads to the fatal errors.
This leads me to believe that somewhere someone modified their shared parameter file manually, changing the phase parameter from "Number of Poles" to "Integer" in the txt file. I have run into this same parameter from multiple manufacturers, which is curious.
If someone comes up with a better solution, I would sure be interested in hearing it.