Howdy pdxkelly!
Based on your post, I can see that you're running into an issue with getting a large movie onto your Mac. I can certainly understand wanting to move it to the Mac so that it wasn't taking up so much space on the iPhone. Thank you for the steps that you've already tried. Let's see about getting this transferred over to your Mac without the error messages.
The first thing that we need to do is make sure that you have plenty of space available on your Mac. A lot of times the error code is caused when it runs out of space to store it. To check the storage space, click on the Apple logo in the top left of your Mac and then click on About This Mac. Once the window comes up, click on the tab for storage and make sure that there's plenty of space. Since the space it uses depends on your resolution settings, a good idea would be about 130 mb per 1 minute of video. That would mean that you need about 12 gb of free space to be able to import it.
If there's enough space, then the next thing that we'd want to do is make sure to close out of all open applications, the ones with black dots under the app icon in the Dock. Once they're closed out of, restart the Mac by clicking on the Apple logo in the top left and then on Restart. After it comes back up, try to transfer it over again.
If for some reason it still isn't allowing you to transfer it over, we'd want to create a new user on the Mac and then see if it'll let you transfer it in that user. If it does allow you to do it in the new user, then you should just be able to drag and drop the file from that user to your user. To create a new user, follow the steps in this article: OS X El Capitan: Set up users on your Mac
Make it an awesome day!