"Why did he not speak to her on the phone?"
Translation:Pourquoi ne lui a-t-il pas parlé au téléphone ?
"Pourquoi n'a t'il pas parlé avec elle au téléphone?" is also a fine solution.
Sorry aklamo, your answer isn't grammatically correct. After question words such as pourquoi we either use inversion with a hyphen or est-ce que and the normal order. The indirect object to her, translated by lui, should go before the avoir verb.
Isn't this correct - "pourquoi il ne elle parlait pas par telephone"
Sorry, not correct. Same comments apply to you, hybridpro, as to aklamo. Elle is the subject pronoun, used at the beginning of a sentence. Lui is the correct translation of 'to her'. Au telephone is also more used.
I suppose this solution isn't correct either: "Pourquoi lui n'a-t-il pas parlé au téléphone?", is it?
Not correct, anetbok. Even in questions, the ne comes before any pronouns like lui, just as the pas goes in front of the past pasticiple parle (excuse lack of accents).
il a parle is usually translated by the past simple: did he talk/ he talked. il parlait is the imperfect and usually used when an action is repeated in the past or was going on for a while. A common translation using a sentence similar to above might be 'why wasn't he talking to her on the phone?'