How do I prevent the ring sound from coming through if I use my phone to play music to a Bluetooth device.

You would need to put the iPhone on Mute. However, you would not hear any notifications at all. If you do not mind not getting any notifications, you can also put your iPhone on Do Not Disturb and that would prevent all notifications. While on Mute and the iPhone vibrates, you may still lose music for a second or two.

Hello,

When you play music or other sounds with a Bluetooth speaker attached, any sound including rings will play through the speakers.

To stop the rings, set the mute slider on the left side of the phone. The Bluetooth speakers will still work.

Good luck.