Apart from the above mentioned solutions, there's also an alternative way: you can sync photos you put in a folder through iTunes, though the dedicated section in the syncing panel. Even if you can in this way store photos on your iPhone from the PC, note that you won't be able to delete them directly from the phone (you have to delete the pic on the PC folder and then sync).
Also, I'm not sure if the actual panel is present/functional in case you are using iCloud Photo Library
10-30-2016 04:39 PM