I can’t access my locked notes on my phone

You will need to remember the original password or you won't be able to unlock the notes.

You can change you Notes password, but If you forgot the password, Apple can't help you regain access to your locked notes. You can create a new password, but this won’t give you access to your old n

See -> How to lock or unlock notes on your iPhone, iPad and iPod touch

How to lock or unlock notes on your iPhone or iPad – Apple Support (UK)

• Apple doesn't have access to locked notes and can't help you access them if you forget your Notes password. If you forget your Notes password, resetting the password won't give you access to previously locked notes. If you reset and then create a new Notes password, that will only allow you to lock other notes.