Itunes music

You’ll see that message if you’re using iTunes Match. The song that you’re seeing isn’t actually the song from the CD but just the title and the Music app is not able to match it with the iTunes library. You will have to make sure the CD in question is selected to sync with your iPhone when it is connected to the PC/Mac that contains the CD.

What format are the songs in? Are you able to add the songs to your iPhone/iPad i.e. do they show in the respective Music app on the devices? Do you get an error message when you try to play the songs?

You shouldn't see this message with music you synced from your library to your iPhone. You should only see it if you use iTunes match/iCloud Music library and Apple tries to match the music with their own library. I have the same issue with some of my music and Apple told me on the phone that the only way around this is to add the actual songs to my iPhone. However to be able to do that I would have to turn of iCloud Music library and I haven't felt like messing with that yet. This site might help:

https://appletoolbox.com/what-to-do-if-a-song-is-not-currently-available-in-your-country-or-region/