iPhone Sync (via cable/Finder): Documents & Data wants to eat up iPhone storage

Hello, I'm trying to sync some Books files between from my MBP to iPhone via a USB-C cable, but in the storage preview, it seems like sync wants to download "Documents & Data" onto my iPhone eating up all of its storage, and I can't find a way to toggle this off.

Note: As the Books files are custom imported rather than purchased on the app, I need to sync these rather than re-download from Books on my iPhone.

I have iCloud+ and use iCloud Drive primarily for backup, files and my photo library (400GB+).

Devices concerned:

iPhone 13 Pro, iOS 17.02

M2 Macbook Pro, Sonoma 14.0

What I see when I connect my iPhone:

Current iPhone storage:

I don't think it's Photos as the second screenshot would suggest I'd need to switch off iCloud Photos in order to sync those from Mac to iPhone. Same for Music, which I switched to recently so my library is small:

The Movies, TV Shows, Audiobooks and Books tabs have sync switched off and don't show any files:

The Files tab shows a handful of cross-device apps like Numbers with available files in kB, or not showing anything at all, so I don't think it's that either:

The only other guess is that it's attempting to sync iCloud Drive files stored locally on my Mac to my iPhone, but that seems like bizarre behaviour - also, the sync preview shows a larger amount of files than are actually in my iCloud Drive:

System Settings shows:

Toggling various sync options does not change this.

How do I troubleshoot this and prevent Documents & Data syncing to my iPhone?

Thanks in advance!