Hello TT Bob,
I have this same issue. I think it's something Apple will need to fix. It definitely involves HEVC videos.
As a temporary work around, if you really want those videos on your phone now, this worked for me:
1. Export the videos to a folder on your desktop
2. Drag and drop that folder onto iTunes to import them
3. Make a playlist of the newly imported videos
4. Set iTunes "Movies" sync settings to "Include Movies from Playlists," and make sure your new playlist is checked.
5. Sync your phone
6. Look in the TV app on your phone in Home Movies
*The artwork may be completely mungged - mine showed as a Glen Campbell album - but the video plays fine. If this really bothers you, you can go back into iTunes, set poster frames for each wrong artwork video and sync again. I had to do this several times before the fix took
*This is really kludgey and results in you having 3 copies of big files on your computer… one in Photos, one on your desktop, and one in iTunes, which is why I recommend the playlist. Once imported to iTunes you can delete the desktop folder, and once Apple fixes the issue, we'll be able to delete the files in iTunes and sync them from Photos normally, I hope.
*You can go in to Settings>Camera>Formats on the iPhone and choose "Most Compatible" and the video syncing should resume just fine. Once Apple fixes this, I think we'll all be happier with the HEVC format.
*I'm not deleting the movies from Photos because I believe that ultimately we are going to want the HEVC versions of the movies. If you don't care about that, you could go one more step and delete the HEVC movies from Photos and re-import the movies that iTunes converted to H.264 when you imported them.
[Just in case anyone from Apple happens to see this, I need to say that even as a die hard Apple fanboy since 1982, I find the sloppiness you guys are showing in the last few weeks to be heartbreaking… and inexcusable given the premium we all pay for Apple products that are supposed to "just work."]
Rob