I just read this one. The other thing that's going on is that Stephen has a secret mission that requires him to be put on shore in France, so he wants to do that during a new moon. The question is Stephen's adorable way of "encrypting" that question so as not to reveal the mission to the rest of the crew.

Imagine that you were in a big meeting and you wanted an excuse to leave, so you whispered to your co-worker "Do you think my phone can receive messages in this room?" And he replied "Phones are the foundation of modern telecommunication infrastructure and we're in a large city, I assure you that you will promptly receive any messages that are sent to you."

Funnily enough I think it is much less funny out of context. It is an in-joke that Stephen has picked up very little of nautical life, despite being on ship for many years.