How can I download my music back onto my iPhone?

Redownload movies, TV shows, or music

https://support.apple.com/en-ca/HT201272

Before you can redownload items that you bought from the App Store, iTunes Store, or Apple Books, follow these steps:

• Sign in with the Apple ID that you used to purchase or download the item originally. If you’re not sure what your Apple ID is, we can help.
• Make sure that you have the latest version of iTunes, iOS, macOS, and tvOS.

On an iPhone, iPad, or iPod touch

1. Open the iTunes Store app.
2. On your iPhone or iPod touch, tap  More in the menu at the bottom of the screen, then tap  Purchased. On an iPad, just tap  Purchased. 
3. Depending on what you want to redownload, tap Music, Movies, or TV Shows. If you use Family Sharing, tap My Purchases or choose a family member’s name to see content that they purchased.
4. Find the movie, TV show, or music that you want to redownload, then tap it. 
5. Tap  to the right of the title. The movie, TV show, or music downloads to your device. You can find movies and TV shows that you redownload in the TV app§ or Videos app, and music in the Music app. Don't see the item that you purchased?