iPhone stopped streaming

Photo streaming to and from my iPhone 4 (iOS 7) and iPad Mini (iOS 8) was working well, but suddenly photos taken on the iPhone will not stream. Furthermore, in iCloud the phone is no longer listed under "my devices" and the only photos in the iCloud album are those from the iPad. Yet photos taken on the iPad DO stream to the iPhone, so something is connecting the two devices. I have already checked the relevant settings on the phone, and all iCloud functions are turned on (as they have always been). The only change I know of is that the iPad is now using the latest OS 8, but the new OS does not support iPhone 4. Why is the phone still able to receive streamed photos but not showing up on iCloud, and how can I get photos streaming again from the phone?