Sorry for not being more elaborate. I was going for brief and concrete; obviously I failed miserably.
It is as rockmyplimsoul wrote below. I didn't choose to upgrade my notes app, when upgrading to ios 10, since I was afraid I'd loose the other notes that weren't in iCloud, and also I hadn't upgraded my macbook air, 11-inch, from mid 2012 yet (and they would therefore, as I recall, no longer sync if I did), since I didn't want the hassel and loss of performance that comes with it (now however I'm forced to).
So now that I've upgraded my macbook I thought I might as well upgrade the notes app. But the reason for postponing it in the first place more or less remains –will I lose the files not uploaded in the cloud? There is, however, an option whereby you could move the files "in my iphone"-folder to a folder within the iCloud account (which would solve my doubts). I have created a folder in notes on my macbook for this purpose but it doesn't show on my iphone (since, probably, the app is not upgraded yet).