well, there's Auden's Greek Phrase Book
). I haven't used this enough to speak for its usefulness - my impression is some of the material is fairly complex, perhaps not what you want at this point.
If you read German, you could also take a look at Altgriechisch im Alltag
) which has good coverage of basic idiomatic phrases.
IPHIGENIE: Kann uns zum Vaterland die Fremde werden?
ARKAS: Und dir ist fremd das Vaterland geworden.
IPHIGENIE: Das ist's, warum mein blutend Herz nicht heilt.
(Goethe, Iphigenie auf Tauris)