Sophie Neveu's trying to convince an infuriated Bezu Fache that the numbers Saunière wrote before he died were basically a numeric joke.
When put in order, they form the Fibonacci sequence, a really famous mathematic progression in which each term is equal to the sum of the two preceding terms. (Yup: there's such a thing as famous mathematical progressions.)
Fache can't accept that Saunière would take the time to goof around with numbers before his death.
Neveu acts indignant about Fache's rejection of her theory and storms off.
Fache turns his attention to Langdon, who is still listening to his messages that Fache believes are from the U.S. Embassy. This further enrages Fache, and he's determined to catch his man tonight.
Langdon ends his phone call looking very shaken. He asks to use the rest room for a minute to gather himself.
Fache is fine with it, because all possible exits are sealed and guarded by his men.
Fache lets Langdon take his moment while he goes back to the command center in Saunière's office to yell at Lt. Collet for letting Neveu interrupt his interrogation.