Thanks, Juliette, for those cute pictures. Do you remember the pictures of P. Caroline in the Paris metro ?
A little cultural tidbit: Taxis in Paris used to be prohibitive and not easily available. They still are not as easily available as in New York or London. It also used to be more expensive to take the bus than the metro in Paris, and it was often the wealthier inhabitants who took the bus, as well as schoolchildren and the elderly. The bus network is so well designed, covering many streets and with many bus stops that it is more fun taking the bus (you see a lot of Paris that way) and more practical than the metro or taxi (if you are not in a hurry). The girls from the sixteenth, seventh and eigth arrondissements (the poshiest districts in Paris) are well-known for travelling by bus and numerous French films use that custom to describe encounters, flirting, etc.
Obviously, in these pictures, Charlotte is keeping other people at bay with a real or fake phone call. Who could blame her ?