iPhone not syncing with iTunes library.

I uploaded some old CDs into my iTunes library on my MacBook. This worked fine. I followed the instructions here (https://support.apple.com/en-us/HT210611) to sync them with my iPhone. Unfortunately, nothing about my music library is changing when I sync with my computer. The CDs I added are not showing up. I also tried to simply drag the CD content onto my iPhone on my computer and that worked for 2 CDs but not the others. Any suggestions?