Using Swift 4, Firebase Auth, Firebase Cloud Firestore.

I have a chat DB and a user DB. I am using phone authentication with Firebase and am saving the UID to store for each user in the user DB. For each chat DB, I am storing the current user's UID to allow a lookup to happen. It's here where I am stuck. Is there anyway I can get all chats from a specific user if the sender ID is a attribute to each document in the chat DB?