。
Please call me at 9 tomorrow morning.
Literal
Tomorrow [possessive-の] morning 9-o'clock [at-に] phone [object-を] please-give.
下さい (ください) alone, without a preceding ~て form, is the request form of the honorific くださる — literally 'please give me X.' Here it requests a phone call as an object: 電話を下さい = 'please give me a phone call.' Contrast with 電話してください, which would use the て form for the same meaning.