Currently dealing with the same issue.
i don't sync/ download photos too often.
Started with my old 4s three days ago, because I was getting a new SE delivered.
I tried the listed remedies: update phone to 9.3.2, update iTunes, restart phone, restart Mac, soft reset phone, pram zap, smc zap, repair disk permissions, turn off iCloud, turn on iCloud, turn off Drobbox photo synch, rub belly and head counterclockwise while holding down CTL-shift-option-space-ESC keys (tough!). Tried Photos, Image Capture, iMovie, iPhoto. Nothing recognized the camera, even as iTunes synchs up fine.
BTW using Yosemite, and Apple tells me iPhoto will NOT work under El Cap. Could be wrong, that's what the rep said though FWIW.
Got the new SE with all my pictures transferred onto it. Expectation was, problem solved as issue would have been with old phone. However, issue persists even with the new equipment. It is apparent there is some software issue or conflict causing the problem. Seems that delete and reinstall Photos would be next but that is only possible with full El Cap upgrade which I am reluctant to do.
i am currently on my third Apple phone support rep. First two were cordial but ineffective and as puzzled as me that the "import" box does not appear nor is either phone visible as a "device". Today was kicked up to "senior support", also ineffective in solving the problem but spent much less time with random clicking around on my screen before surmising "might have to get the engineers involved".
Meanwhile was able to upload everything to Google Drive via there Photo app.
Very, very odd that the Google software works better than the Apple software.