How Do I Add An MP3 Audiobook To iTunes To Sync To My iPhone?
Launch iTunes on your Mac and add the MP3 audiobook file via drag and drop or by going to File > Add to Library (Command-O). Once the file has been imported, find it in iTunes, select the item, and go to File > Get Info (Command-I). Click on the Options tab and under Media Kind select "Audiobook". iTunes will now treat this file as an audiobook rather than as a music file, ensuring proper playback on any of your devices.