Could you repeat that? I sometimes need to say the equivalent of Sorry, could you repeat that? I have found one comfortable phrase (for me) to handle this situation but would like to learn other phrases to use in this case. 

When speaking Cantonese I might say something like:


  nei gong matyeh, ting m doh (你講乜嘢, 聽唔到 lit: what did you say, I didn't hear everything)


I'm sure that Mandarin and maybe even Cantonese speakers would not say this phrase. But people get my gist as a non-Asian. I'd be grateful for any wisdom shared so that I can communicate this concept better.
There's no real special phrase for this situation, unlike English's "I beg your pardon". Therefore, anything conveying the sense of "please repeat" or "I didn't hear" works. For instance, as is increasingly the case in English as well, normally you could just say "what?", 什麼?. 

To be a little more preciser, as well as polite / less familiar, you could say 對不起, 我沒聽清楚, "Sorry, I didn't quite catch that." And then you can ask them 可以再說一遍嗎?, "Could you repeat that?"

Really, just about any translation of what you'd say in English would work. Since there's no specific phrase, as long as the sentence is grammatically sound and makes sense, you'll be understood just fine.