LG Trax CU575

I recently installed a the Pioneer DEH-P7900BT deck for my car. The kid at best buy said that i should be able to listen to the music player on my phone through the bluetooth deck now in my car. well it makes phone calls great (through the stereo system), but while the phone and deck is sync'ed with my mp3 player function running, it still is only playing through the crappy phone speakers and not through my car speakers? any one nerdier than me want to educate me out there? Thanks for your time... it's driving me nuts 🙂