You wrote: "and my iCloud account mirrors what is on the phone, which doesn't make sense."
But that is exactly how iCloud is supposed to be working. It is a syncing service, keeping the Photos Libraries on all your devices identical. With iCloud Photos enabled, you should always be seeing the same photos on all synced devices. When you import new photos to Photos on one of your devices, they will be synced to iCloud and from there to all your other devices. And when you delete photos on any of your devices, the photos will be deleted from iCloud Photos as well and from all other devices. With iCloud Photos you are essentially have one Photos Library in iCloud, that is mirrored on all synced devices.
I went to forward some photos to a friend today and hundreds of my photos have disappeared. I have a few photos from last week and then only photos from November 2023.
Did you delete photos from any of your devices, assuming they have been saved to iCloud or would be staying on your other devices?
Perhaps the dates on the photos are wrong and the missing photos are now sorted differently in "Library > All Photos". you may want to check, if the photos are appearing in a different month or year than you are expecting.
Photos may also appear to be missing, if a Filter has become enabled. While viewing an Album or "All Photos" tap the three dots and then "Filter". Is it set to "All items"? If not, change it to "All items".
if you have not only been using iCloud Photos but the Shared iCloud Photos Library as well, ensure, that the selector for the library has been set to "Both Libraries", not just your "Personal Library".
