Hi fil_p,
Thanks for reaching out to Apple Support Communities.
It sounds like you’re having an issue with viewing a locked note on your iPhone.
We’re happy to assist.
We recommend checking out the steps in the section titled "Open a locked note" from the article here: How to lock or unlock notes on your iPhone or iPad
Open a locked note
1) Tap the locked note.
2) Tap View Note.
3) Use Face ID or Touch ID, or enter your password.
Your locked notes stay open for several minutes, making it easy for you to jump to another note, copy and paste information from other apps, and more. If you close the Notes app or your device goes to sleep, the note is locked again.
We recommend the steps above because they directly address the issue you initially posted: you cannot view your locked notes.
Should the issue continue, follow up with the steps in the section below.
Reset your Notes password if you've forgotten it
To unlock a note, you need to enter the password that it's locked with. If you've forgotten your Notes password, Apple can't help you regain access to your locked notes. You can create a new Notes password or use your device passcode instead, but this won't give you access to your old notes. If you set a new Notes password or switch to your device passcode, you can protect any notes that you create going forwards with the new password.
If you have multiple Notes passwords, you won't be able to tell which password you should use when you look at your Notes list. When you open a note locked by an old Notes password but you enter your current password, you'll receive an alert stating that you've entered the wrong password, with a hint for your old password. If you enter the correct old password, you'll get the option to update that note's password to your current one.
To reset your Notes password:
1) In the Settings app, tap Notes. Then tap Password.
2) Select the Notes account you want to change, then tap Reset Password.
3) Enter your Apple ID password, then tap OK.
4) Tap Reset Password again.
5) Use your device passcode or enter a new password and password hint. Tap Done.
Please let us know the outcome after giving the above steps a try.
Cheers!