Hello John Comeaux,
Thank you for using Apple Support Communities!
It sounds like you are wanting to import a trailer you started on your iOS device to iMovie on your Mac but the item is grayed out when you are in iMovies File>Import>iMovie for iOS Project.
It looks like that function is intended for Projects, and not for Trailers with info from this article:
iMovie for iOS (iPad): Export a project to iMovie for OS X
You can export a project (but not a trailer) you create in iMovie for iOS to iMovie for Mac, where you can continue to work on it.
It appears this is expected behaviour.
If you would like to watch your trailer on a Mac you can share the project to the Camera Roll and then import that file to the computer the same way you would import other video.
iMovie for iOS (iPhone, iPod touch): Share projects and trailers to the Camera Roll
All the very best,