You may try few things to get this issue resolved.
1. Please check the Read & Write permissions for all the Lightroom folder in both user and system library, it should be set to full access.
2. Same goes with iPhone folders.
3. Turn off the GPU from the Lightroom preferences.
Open Lightroom > Preferences > Performance tab > Uncheck the GPU > Restart Lightroom.
I searched for all folders in ~/Library and /Library containing "lightroom" or "iphone". All where read/write enabled.
Turned off GPU and restartet LR.
Started import 12:10. Now, more than 15 min later no progress.
And I can’t end LR correctly. If I say "quit" it asks me, if I want to end import. If I say "yes", LR gets unresponsive and I have to kill the task.
I'm having the exact same issue. Same configuration, except iPhone 7 and Mac OS Sierra 10.12.6.
My phone has thousands of pictures on it, but even trying to import only two pictures stalls.
I deleted all photos from my iPhone (something I never wanted to do; my goal would be to keep as many photos on the phone as possible memorywise) and now import seems to work fine (tried it only a few times). Before that, I had only about 3k pics on the phone. I will keep watching this,