Books audiobooks syncing Mac to iPhone issue

Whenever I try to load new audiobooks from my mac books library to my iphone, I need to do the sync process two or three times before the audiobooks are transferred. This occurs whether I do it tethered or wirelessly.

It goes like this: I open the iphone in the finder sidebar location and then select audiobooks. The ridiculously small audiobooks selection window opens and I deselect books that I've listened to and then select the new ones I want to add and then click sync. The mac asks to backup the phone, and I say no, then my iphone asks me for my iphone code and then the mac wants to back up the phone again, I say no again, then it dithers, gathers diagnostic data and transfers that and then it starts to prepare to transfer the data files (audiobooks) and then abruptly ends the process.

So I start the transfer again with the same prompts and code input only this time it deletes the audiobooks I've asked it to remove and then sometimes it will transfer the new audiobooks but generally it will just end after deleting, requiring me to start the process once again and if I'm lucky, the files will get copied over. Why? Why is it so hard to an audiobook from my mac to my iphone?

Please tell me I doing this wrong and there is a super easy solution. Cheers.