Hello mrrviolao,
Thank you for participating in the Apple Support Communities! We see that you have a question regarding how much storage Music is using on your iPhone and we'd be happy to help.
Did you recently set up this iPhone, turn on Sync Library, start an Apple Music subscription, download new music, or make any other changes on the iPhone? From what you've described, the 58.88 GB that you're seeing should indicate how much storage is actually being used on the iPhone for downloaded music, however, it's possible some of this music has not finished downloading to your device.
When you go to Settings > Music > Downloaded Music, does this number match what you're seeing in the other location? Is Optimize Storage enabled for Music?
Let us know what you find and we'll go from there.
Take care.