I've actually been struggling with the same issue that you are talking about. Good new and bad new.
The good news is that with the new operating system releases on the Mac and iPhone, audiobooks are moved into the books app on both the Mac and iPhone. You can create a collection on your Mac in books, and have that collection show up on your iDevice. If you export those audiobooks to your iDevice, they show up in the correct collection. You can manually sort audiobooks in a collection. For example, I have a collection for both the Dresden files and Tanya Huff's Blood series with the books manually ordered in the correct order. I've played with it in the Beta with a limited number of audiobooks on my laptop and iPad mini and it appears to work. I'm looking forward to the actual release of iOS 13 (today) and Catalina (early Oct) to test it out with my main desktop that has all my audiobooks and my iPhone, which I use to listen to audiobooks in the car.
Bad news. Book collections aren't a playlist, so it doesn't automatically go from one book to the next. I have CarPlay in my car, so I use that and select the next book when a book finishes. You will have to manually select the next book on your phone if you don't have CarPlay, something you normally don't want to do while driving.
One of the other threads gives my various posts on my struggles with listening to audiobooks in my car.
|