This is the airline pilot in me... If I was a crew member on the aircraft in question, I would NOT operate it until maintenance removed the phone. My justification would be that electronic device is not stowed properly, is located in a potential hazardous location that could interfere with possible aircraft systems (all depends on the type of aircraft and location), and there is always the risk of battery fire. This is a major safety violation if the crew elected to depart knowing this situation.