Hello GHB2020,
Thank you for using Apple Support Communities! I understand that you can hear while on a phone call using Jabra Bluetooth headphones paired to your iPhone, however you're unable to hear music through the headphones. I would be happy to help point you towards a resolution.
The next time that you play music on your iPhone, I would like to have you open the audio card, then check that your headphones are selected as the output device:
Use and customize Control Center on your iPhone, iPad, and iPod touch - Apple Support


"Control audio
Press deeply or press and hold the audio card in the upper-right corner of Control Center to quickly play, pause, and control the volume of your favorite song, podcast, and more.
Tap
to switch the audio output to speakers, headphones, Apple TV, or another audio device. You can also choose to play the same music across multiple speakers you have set up in your home.
You might also see cards for nearby devices that you can control audio playback for. Just tap a card to control audio for that device. You can also use the cards to create a shared music queue with friends."
If you're still not able to hear music playing, could you let us know what model of headphones you're using? What iPhone model and iOS version do you have as well?
Cheers!