all my music disappeared from my phones how get it back

Are you subscribed to Apple Music or iTunes Match? If so, see the replies to this question:

how do i get music back on apple music..all of my music disappeared

If not, and if you have the music in your iTunes Library, then sync your device with iTunes:

Sync your iPhone, iPad, or iPod touch with iTunes on your computer using USB - Apple Support

Sync your iPhone, iPad, or iPod touch with iTunes using Wi-Fi - Apple Support

iTunes for Windows: Syncing overview

iTunes for Windows: Sync iPod, iPhone, or iPad

You can also download your previous iTunes Store purchases directly to your device:

Redownload music, movies, TV shows, apps, and books from the iTunes Store, iBooks Store, and App Store - Apple Support