Not this article.question. Notes disappeared from IPhone 6 how to get back
Notes disappeared on my IPhone 6 how to I get it back. Has notes I really need.
iPhone 6, iOS 11
Assuming they are iCloud Notes;
First log into iCloud.com in Safari or preferably a browser on a computer and see if they are in iCloud.
If not they are gone.
If they are there then in phone
Settings, yourname, iCloud
Turn Notes on.