Getting music from my Mac to my wife's iPhone

20 years ago I ripped my entire CD collection and the music is now on my Mac in my iTunes media and represented in my Music Library. At the time, I also created some CDs for my wife. My wife would now like to have those CDs replicated on her iPhone, which currently has no music whatsoever on it. She would like to listen to the music while she is in her car.

I created a playlist mimicking each CD in Music. I plugged her iPhone into my Mac using a lightning cable. I can see her phone in Finder and on the left window in Music. However, when I try to drag the playlists onto her phone in Music, nothing happens.

I'm not looking for her to have my entire music library on her phone, just the songs that are in the playlists. All of the songs are from ripped CDs (none has been purchased from Apple Music). How do I accomplish this (what I thought would be easy) task? Is it even possible? Is it possible to manage the music on her phone without syncing it (I don't want all my music on my Mac replaced with the music on her phone (which is none))?

I have tried all kinds of searches, but nothing seems to apply. Thanks in advance for any help.

Both the Mac and her iPhone are up to date with the latest macOS and iOS systems.