In reply to Jamming Dodger: > What difference does it make if she's on the phone or talking (albeit loudly) to someone sat at the same table as her?
You might still feel inclined to ask them to keep their voices down, since not everyone in their immediate vicinity wants to be party to their conversation.
Coming back from London recently in the quiet coach, we asked a man and a woman to keep their voices down. In point of fact it was only the woman that was the problem. You could hear when the man was speaking, but not what he was saying. She, on the other hand, kept fog-horning complaints about her work, the industry she worked in, the town she lived in and...well, pretty much everything about her life. After being asked to help the rest of the people in the carriage avoid eavesdropping on her, rather than just keep her voice down she slunk off to a different carriage in a somewhat graceless fashion. I rather suspect her male interlocutor was secretly a little relieved to have the conversation drawn to a premature close.