GPG Plugin does not ask for passphrase
I just installed the GPG plugin and it seems to work since the buttons encrypt/sign show up and turn green when I add recipients where I have the keys stored in my keychain.
I don't have my key's passphrase stored in my Mac's keychain and expect the application to pass the passphrase request along to the GPG keychain tool as the Mail plugin does.
Bruno Perles commented
GPG plugin is old, I think it's no more maintained anymore no?