3.5 mm audio jack

Okay, so I have an old FM transmitter that I want to use in my car, so I can play tunes off my phone. Unfortunately, the transmitter doesn’t have Bluetooth capability AND has a 3.5 audio jack for whatever device your wanting to play music from....but I have an iPhone and honestly don’t want to...

I'm trying to get my desk set up at home so that my one set of speakers will play either the audio from my work laptop, or the audio from my home PC. I have both systems on the same desk and I use HDMI switchers and a USB switcher to switch my monitors, keyboard, and mouse between the two...