For this use of por, think about the transmission of anything but people. Often the translation of ‘by’ or ‘via’, you can use por here to express sending messages, packages, or ideas.
English: I’m speaking on the phone with my mum.
Español: Estoy hablando por teléfono con mi madre.
English: Lara sent me my results via email.
Español: Lara me ha enviado mis resultados por correo electrónico.
English: He sent the package by plane.
Español: Él envió el paquete por avión.
Before moving on, typically when you are talking about things they go por avión (by plane) or por coche (by car). But, when you are talking about people they go en avión (in a plane) or en coche (in a car).