1. You can't leave a message.
2. Once you get someone on the phone, yes he/she speaks English.
3. They do answer the phone. I literally caught them a week ago. It is best to call shortly before and after mealtime, such as within 30 minutes before and after. Such is my experience.
Make the very best set of reservations you can before leaving home. When you get to Paris and you still haven't a gotten a Frenchies' reservation, walk over during serving time and ask if he has anything available during your stay. Take whatever he offers and bag the runner up. That's what I do.
One eager guy reported here that he had his hotel send someone over to grab a reservation. That's a REAL chowhound!