Thanks for getting back to us pturner13,
Let's have you do this:
- On the Mac, open iTunes and click on Songs to view all the songs in your library.
- On the left side of the song title, do you see a checkbox? If you do, make sure all the songs have a check in the box.
Any songs that do not have a check in the box may not get synced across devices, such as your iPhone.
If you don't see the checkbox, then click on iTunes in the top Menu bar > Preferences > General, and make sure "Songs list checkboxes" is selected under the "Show" section.
Try re-syncing after that and see if that resolves the issue on your iPhone.
If the issue persists, then reach out to Apple Support: Get Support
Cheers!