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Please don't call late at night.
Literal
Night late phone [obj-を] don't-do-[negative request-ないでください].
~ないでください is the polite negative request ('please don't X'), the negative counterpart of ~てください. 電話する is the suru-verb form; 電話をしない separates 電話 and する, a slightly more analytical structure with the same meaning.