Why is が not being used in this sentence?


> A: あの～、すみません。  
>  B: はい。  
>  A: このへんにこうしゅうでんわはありますか。  
>  [Image](https://i.stack.imgur.com/OBP9K.png)

In the third sentence, は is used instead of が, but こうしゅうでんわ is something new
being added to the conversation, which is a function of が.

