How to stream music from your phone in an older car

Upgrading your car stereo capabilities on the cheap. Story time: I've got an older car, a 2001 VW Jetta, that still runs great but lacks some of the modern amenities that I would prefer to have in my car. Most notably, my car stereo still prominently features a cassette deck along with FM/AM radio. Yeah, I'm pretty sure this setup was out of date back in 2001. I'm well past using physical media for my music, so I needed to find a way to transmit the music from my phone to my car stereo. Ideally,...