I can only view device-size photos, the full-resolution images are not downloading. Please help!

I can only view device-size photos on my iPhone, the full-resolution images will not download. The white loading circle appears but it remains empty, denoting that the photo is not downloading. This is extremely frustrating as it makes using iCloud for photo storage almost useless. It's also frustrating when you want to watch a video, but it takes forever to download if at all.

Apple, please fix this. This is not feasible.