Rashi on Numbers 12:6/רש"י על במדבר י״ב:ו׳

1שמעו נא דברי HEAR, I PRAY YOU, MY WORDS — The word נא is always an expression of entreaty (Sifrei Bamidbar 103).

2אם יהיה נביאכם means, IF THERE WOULD BE PROPHETS TO YOU (i.e. if you had a prophet — if you could show one to me).

3ה׳ במראה אליו אתודע This means: the Shechinah (the Divine Glory) of my Name does not reveal Itself unto him in a “transparent glass” (i.e. a direct revelation), but in dreams and visions (cf. Sifrei Bamidbar 103).