Kikko2020,
Thanks for checking where those notes are stored. We'll need to move those notes to the iCloud folder, so they'll sync. First and foremost, before we move anything, please be sure you have a backup of your iPhone. Since the notes are currently stored on your device, they will be stored in the backup. You can make that backup to a computer or to iCloud if you have enough space.
How to back up your iPhone, iPad, and iPod touch
Now for the moving of the notes. The easiest way to do that is:
From the Notes app tap the back arrow at the top left until you're looking at all your folders
Tap the Notes folder under On My iPhone
Tap the circle with the three dots at the top right
Choose 'Select Notes'
Tap the circle to the left of each note you want to select
At the bottom choose Move
Select the Notes folder under iCloud
This should move your selected notes to the iCloud folder and then as long as Notes is enabled in Settings > your name > iCloud sync them with iCloud.
Let us know if you have any issues or questions.