Hi CLL1972,
Without the steps currently being taken to play music on his iPhone, specific recommendations on what to change would not be possible.
It is worth noting however that some vehicles will automatically play music upon connection starting with the first track alphabetically. If that is the nature of the concern, consulting with the car radio manufacturer would be advised.
For general playback, if a previous song was paused that should display at the bottom of the Apple Music screen with a play option to resume. More information on controls and options can be found at Listen to music and more in the Apple Music app.
Regards.