If you are using Ubuntu on your computer, you may be struggling to add music to your iPhone. Don't worry, there is a simple solution and it is called VLC.
Go in the Apple AppStore and look for VLC. It's free and those work great for handling media files.
Once installed on your iPhone, open the app and look at the left side, you can enable WIFI sharing.
Note the provided URL and on your Ubuntu computer, open your browser to reach that URL.
Then simply add your music to the VLC app using the webpage you'll see in your browser. It's easy to use and works with any computer.
You'll then rely on VLC for your musc listening instead of using the stock music app from Apple.
As a bonus, VLC can play may file format and you can also rely on it for your movies encoded in MKV or other unsupported encoding by your iPhone.