Music on iPhone vs Apple Watch on runs

I've downloaded music to my Apple Watch 5 cellular so that I can leave my phone at home when I go for a run. I connected my AirPod Pro with the watch. When I use the Music app on the watch to start the run playlist I have downloaded it works. Then I start my run. As I get farther away from my phone, the music breaks up for a few seconds, but is then ok. My route takes me on a loop past my phone though. And when I get close to my phone again, the music stops playing and I can't find any way to start it again. I've tried turning off Bluetooth on my iPhone to stop it, but that doesn't work either. Any thoughts?