There are a few ways to express a lack of understanding and to request additional information. The most common ones are stated, but you can also say “Excuse me” or simply “I can’t hear you.” In a more formal situation, try saying “I’m sorry?” or “I beg your pardon?” (with a rising intonation).

 When asking someone to clarify information try saying Can you please repeat that? / Can you spell that for me? / Can you please write down the address for me?

 Cutting out describes a difficulty in understanding a caller due to poor cellphone reception. If you are having trouble understanding the caller, you can also say The line is breaking up / I am losing you. If the phone call is disconnected because of poor reception, you can say The call dropped.

 Talk to you later is the equivalent in a phone conversation of “See you later” in a regular, face-to-face conversation. 

 Reception here means the availability of cellular service, the possibility to receive and give calls on a cellphone. Cellphone reception can be limited in remote areas, inside large buildings or underground (in the subway, for instance).