If the music you want to transfer is stored in your iTunes Library, you may prefer to add music to your Apple iPhone using iTunes. Even if the items are not in the iTunes Library, you can add the content to it and then copy MP3 to iPhone with the help of iTunes.
To sync music to iPhone with iTunes:
Step 1. Connect your iPhone to the PC/Mac. If iTunes doesn’t launch automatically, double-click it to run the program.
Step 2. Click the device icon and click the “Music” option.
Step 3. Choose “Sync Music“. In the popup, click “Remove and Sync” to continue.
Step 4. Select to sync the “Entire music library” or “Selected playlists, artists, albums, and genres“. If you choose the latter, you need to manually select the playlists, artists, and albums.
Step 5. Click the “Apply > Sync” to start adding iTunes music to iPhone.
Step 6. When it has done, go to “Music > Library > Songs” on your iOS device to check the music.
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