Which audio system is it? Is it the 7" screen with basic MBUX function? If it is you need to select each device and assign its priorities, you select which ones are calls and which ones are streaming devices, under sources it should list all devices connected and How (cable, bt, USB1 etc). There is a settings box at the end of each device name you touch/scroll to and you can adjust properties, volume offset/preset etc. Apple devices however you need to pay attention to the order they are connected via USB (I have old ipod and newer ipod touch for streamed content), it will only stream from one and supply power to other. I read this in a manual somewhere but cant find it now.
However, If you didn't get optional Android Auto/Carplay you may not be able to use both, I'm not that familiar with the Sprinter version I'm sorry.