La respuesta es sí. Puedes hacer prácticamente de todo con el teléfono plegado. Te copio un texto de la página de USA de Samsung dónde responden exactamente a tu pregunta. Un saludo.
"The front screen on the Galaxy Z Flip series is called the Cover screen, and it lets you view notifications, battery life, and other information like the time – all while the phone is closed. You can even send messages, answer phone calls, and take selfies from the Cover screen. When the Z Flip is closed, just use one of the simple command gestures, like double pressing the Side key to open the Camera app. You don't even have to open your phone to use Samsung Wallet."
Samsung Galaxy Z flip4 · Puede realizar y descolgar llamadas mientras está plegado?
Respuestas
"The front screen on the Galaxy Z Flip series is called the Cover screen, and it lets you view notifications, battery life, and other information like the time – all while the phone is closed. You can even send messages, answer phone calls, and take selfies from the Cover screen. When the Z Flip is closed, just use one of the simple command gestures, like double pressing the Side key to open the Camera app. You don't even have to open your phone to use Samsung Wallet."