How do I restore Apple Music app and sync songs after accidental deletion?

I had previously, for some time, been successfully sync'ing all my songs between Apple Music on my iPhone and Macbook. I recently accidentally deleted the Apple Music app on my phone and now sync'ing does not restore all my songs -- only a very small portion of them. The others show as grayed out in my playlists and clicking them indicates that "this item is not currently available in your country or region." I have not changed countries / regions and both my Mac and my phone indicate that they are in the United States.

Any help would be greatly appreciated. Thanks.

[Re-Titled by Moderator]