With the new iOs 8.4 update has been moving all audio files into the iBook App and not the Music App. The changes that iBook has made have been the removal of chapter names/references as they are converting into track numbers, the sleep timer, and speed options. To avoid iBook and continue your audiobooks with the Music Player, please follow the instructions below
1. Plug your phone into the computer with a USB cord.
2. Open iTunes and your iPhone/iPad/iPod will appear.
2. Click on the Music icon ( ) in the upper-right corner of iTunes.
3. Click on Playlists in the middle of your screen.
4. Click on + at the bottom left-corner of iTunes to add a Playlist.
5. Click New Playlist
6. Rename your Playlist to the name of your Audiobook.
7. Drag your audiobook files from the fold on your computer (Where you saved the MP3 files of your audiobook to your computer; this is usually the Downloads folder) into the white space in iTunes.
8. iTunes will add the files.
9. Click on your Phone ( ) icon in the upper-left corner of iTunes.
10. Click on Music, under Settings (the top section of categories).
11. Checkmark the new Playlist for your audiobook to include it in your Sync.
12. Click the Sync button at the bottom right corner of iTunes.
Your Audiobook will appear in your Music App