OK, I know, I'm replying to my own post, but I think I found the answer to the problem (see previous post for description). In the new version of iTunes (12.2.1.16), there is a menu bar to the left. On the top is "Settings," followed by a number of selections. Below that is "On my device," followed by another list of selections.
In the top list (under "Settings") is the selection "Music," and clicking on this will produce a screen giving several choices for "Sync Music." On my newly installed iTunes, the relevant selections ("Entire Music Library" and "Selected artists, playlists, albums, and genres") were both turned OFF. Once I clicked the button for "Entire Music Library" my music library immediately started to sync.
NB: My Music Library was successfully re-synced, BUT. I am right back at the situation that brought me here in the first place. After I updated to iTunes 12.2.1.16, I noticed that several of my albums that are in my Music Library on my MacBook Pro do not appear on my iPhone 6 (which is 64 GB and has 25 G of open space). That is still the case, still looking for an answer. I suspect the answer lies in the way that "improvements" in the iTunes database record and display the Music Library, but I can't identify a specific problem.