Let me break down the components:
* Quien: Who (interrogative pronoun)
* Habla: Speaks (verb)
* Contigo: With you (preposition "con" + pronoun "tigo", meaning "you" in this context)
While grammatically correct, this phrase might not be commonly used in informal conversation. It sounds a bit formal and could be interpreted as slightly aggressive.
More natural ways to say it in English:
* Who's talking to you?
* Who are you talking to?
* Who is that talking to you?