How do you come up with one good phrase to describe your music? Here are some ideas:
Email everyone you know, especially your fans, saying you're trying to come up with a single phrase to describe your music, and ask their help. Maybe make it a contest.
Notice what's most unique about you. Do your songs have a recurring theme? Unusual instrumentation?
Find a few 14-year-old kids, and treat them to pizza if they'll sit and listen to a few songs, and describe it for you while waiting for the pizza to arrive.
Read a music review site that's describing music you've never heard. Notice which phrases make you curious to hear more.
Offer to pay a music writer to help you. This is what they do for a living.
When you've got one you like, start trying it out on people. Watch their face. See if it lights up. See if they get curious.
When you've got a great one, you'll know it. Use it for years and years.