iPhone storage

I have an iPhone 14pro 512gb. I'm trying to create a full backup on itunes. I've backed up my iPhones this way many times before, however this time there is an issue with device storage. each time I've tried, the process fails due to running out memory on the hard drive. resulting in an incomplete backup file taking up 280gb of memory. My problem is that according to my iPhones storage in the devices settings, I've only used up 164.59gb with 347.41 free. According to itunes on my pc I have 307.84gb free, with a capacity of 476.72gb. Meaning that 168.88gb is in use. These numbers are reasonably similar to each other, yet when checking the devices storage in windows 10, I only have 128gb free out of 476gb. Meaning I have 348gb used up. How is this possible? Also note that I have 2tb icloud storage, which has 562gb of photos. according to my iPhones storage in the devices settings, theres only 45.09gb of photos on the device (optimised storage is on). but when checking this against what my pc has, it shows 144gb of photos. why is there such a discrepancy? where is all of this memory being used? How can I backup my device without having to get a larger hard drive?