By increasing these values it usually seems to work with most (possibly newer) iPhones:
But there’s still no logical explanation why this issue suddenly appeared only for iPhones. Basically, up until now all image sizes somehow got magically resized, even if they were larger than the defined upload limits, and the behaviour was the same on all devices. But now there are some users that were seeing failures to upload images far below the original (low) max limit, and even with higher limits there are still some problematic images for some iPhone users. Desktop and Android browsers on the other hand continue to have no issues with any image size, including those that are much larger than the established limits.