“how to download PDFs to LOCAL STORAGE ONLY, not to iCloud”

Hi, I clicked unsync Books iCloud (was trying to figure out how to keep files on iPhone only, so it wouldn’t be on the cloud) and then all my PDFs disappeared. I have since figured out how to get the PDFs back (even though they’re not in order for some reason) but still do not know how to keep the PDFs on iPhone local storage only. I have another device that is out of space (usually at 200mb free space) that I use for calls/texting daily so I can’t have all my PDFs taking up space on the iCloud storage since that information is stored on the low-storage iPhone as well and it’s beyond out of space. Most of my Books library consists entirely of my downloaded PDFs so this is an issue.. I really just need to know “how to download PDFs to LOCAL STORAGE ONLY, not to iCloud”