From waaaayyyyy back in the day, most cars didn’t have FM radio, just am band. You could buy an add-on FM band device that would receive the FM signals and then transmit them to the AM radio to hear.

Today, you can get a cigarette lighter powered unit to connect to your phone by bluetooth and then to an unused radio station to listen to your phone. About $10 to $20 or so. They work fine. I have one in a Jeep.