The passphrase is the password used for sync, not the one you use to sign in to Opera. Though I am not a hardcore Opera user, I believe opera would allow any user that remembers their password to get the passphrase. Here’s something that I found on the web.
In your computer's Opera browser:
- Go to Settings.
- Click Advanced in the left sidebar, and click Privacy & security.
- Under Autofill, click Passwords.
I hope it helps!