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general::
Phrase(s): Could I tell him who’s calling? [and] Can I tell her who’s calling?; May I tell him who’s calling?
a question asked by people who answer the telephone to find out politely who is asking for someone. (Him or her can be replaced by a person’s name or by a plural pronoun.) • Mary (on the phone): Hello. Could I speak to Bill Franklin? Sally: Could I tell him who’s calling? Mary: It’s Mary Peters. Sally: Oh yes, he’s expecting your call. I’ll get him for you.
McGrawhill's American Idioms And Phrasal Verbs