Playing music directly from iPhone

I have a lot of music that I've synced to my phone. Sometimes I want to take that phone to work, plug it into a different computer, and listen to the music there instead of using my computer at home (where all of my mp3s are). This used to not be a big deal - you plug in your phone, open up iTunes, and click play. After upgrading to Catalina, I seem to have lost the ability to do this - I can no longer play music directly off my phone through my computer. Any ideas?