PHEV means a lot of things. Toyota PHEVs with e-CVT are simpler than a normal ICE. VW PHEVs where there’s an electric motor tucked into their DSG gearbox - not so much.

Plus more. My Volt had a component fail that was responsible for switching the cabin heater between the battery and the motor, so if I placed the vehicle in pure EV mode then I couldn't heat the cabin, oops!