Hello horsecrazy,
If you are an Apple Music subscriber, you'll want to follow the steps below to verify the Sync Library option is enabled on your iPhone:
1. Go to Settings > Music.
2. Turn on Sync Library. If you don't subscribe to Apple Music or iTunes Match, you won’t see an option to turn on Sync Library.
If Sync Library is updating or turned off, you'll see a message at the top of the Library tab in the Apple Music app.
You can also find those steps in this resource: Turn on Sync Library with Apple Music - Apple Support
If you manually sync your iPhone with your Mac, does that persist after syncing again? Sync content between your Mac and iPhone or iPad - Apple Support
Those steps should help to address any hiccups with the syncing process.
Let us know your results, and we'll keep moving forward from there.