I have this problem as well.
I had too many photos on my phone.
I copied most to an external hard drive, but wanted to do it "the right way" and went to the Apple Store several times.
I knew I needed to download the operating system update, but didn't have enough memory.
I bought phone view but it said it didn't have enough memory to work. I don't know if referring to my iPhone 6+'s memory or the hard drive of my MacBook Air.
I was told on my first trip to the Apple Store to find someone with a computer with enough memory to hold my iPhone's photos. I could only find a mini with 2G ram and was told it would take forever.
Since then, it appears my iPhone has had to 'recover' and is 'restoring' recently, although I am not sure from where, presumably a very old backup in iCloud. Oh no! THEN, the videos seemed to come back.
I went back to the Apple Store to ask the same question and a different Genius told me to use image_capture! Hallelujah. to send the photos THROUGH the MacBook Air into the external hard drive.
But now, image_capture shows fewer photos than my iPhone says it has, shows very few of the thumbnails and shows dashed outlines instead of photos.
I am afraid that the outlines mean that the iPhone has an index of the photos that SHOULD be there but that it can no longer find them. : {
In another blog, there was a reference to a dotted circle in iTunes. I thought that might relate but the instructions to fix that problem were to turn off wifi!?
This is my first iPhone. I apologize for being truly clueless, but this is the only way to learn. ( I thought by now I'd be in Apple heaven! )