Email everyone you know, saying you’re trying to come up with a single phrase to describe your music, and ask their help.
Find a few teenagers, and treat them to pizza if they’ll sit and listen to a few songs, then describe it for you while waiting for the pizza to arrive.
Hire a music writer to help you. This is what they do.
When you’re playing on stage, ask people in the audience.
Read a music review site that describes music you’ve never heard. Notice which phrases make you curious to hear more.
When you’ve got one you like, try it out on people. See if their face lights up. See if they get curious.
When you’ve got a great description, you’ll know it. Then you can use it for years and years.