Thanks, this was helpful.
I had success this morning... All of my photos were imported from the phone (iPhone 5S), and after that was completed, I opened my phone all on the phone, and essentially saw the photos disappear. So... Success!
What did I do differently?
Well there had been two failed attempts (and a few aborted), both of which imported about 250 - 300 photos, then simply quit, and the app became unresponsive, until I had to kill it from the process list (a "kill -HUP" was unsuccessful... The almighty "kill -9" on the process gave it an ugly stop..., but at least didn't effect power on my device. These commands from the "terminals" O/S shell obviously).
As others in this thread have alluded to... This issue appears to be a resource issue on the Mac (maybe even a communication thing between Mac 7 iPhone? Handling lots of images... Probably meant to do in smaller chunks). I had done a reboot before the last failed attempt, so this may not be the smoking gun..., but this time, I rebooted, and made sure everything was closed, verifying in Activity Monitor (i also closed all apps on the phone too).
I then started Photos (on MacBook), with the phone plugged in, and told the app to import all 3,000 or so photos (new only), and "delete after".
I watched Activity Monitor as it completed all of the images, and being a bit anal, I made sure my phone was responsive (although a few times got up & left, and it was locked when came back, so think non-issue...). The activity the whole time was about 50 - 80% on this one app (is probably a good idea to do single-threaded, might be this app just doesn't play well with swapping).
I did not monitor memory usage (my circa-2009 titanium MacBook has 4 GB of RAM), but probably memory-intensive too.
Am liking the fact that after importing all of the images off of my phone, I then went back into Photos on the MacBook and was able to export all of the recent photos to my Apple file-system USB drive, and added the option to create a "Moments" file-folder structure (this will make it easier in the future, should other such Apple App Changes happen for Photos, to organize / and know what images are on that drive, as well as if / when I selectively later decide to import just certain images back to the phone).
I hear the previous poster on the iCloud option. i thought about that, and if this might be an Apple ploy to get users to more use the (and pay for more storage on0 the cloud, so I stayed away from that (although to make sure I had a good backup of my phone before all of this, I did shell out to get the higher-priced option and 200 GB storage, to verify everything backed up before the iOS upgrade).
Hope this helps. This was frustrating, took up too much of resources of at-home life... :-)