In my old job we had a saying: "The biggest threat to security is the perception that there is no threat".
Say what you like about the chances of the phone being suspicious or otherwise, but the Captain had to have the thing removed from the aircraft. The chances of an engine going tits up on takeoff are extremely remote, but we still account for that eventuality in every take off calculation, briefing and sim. Our responsibilities as pilots extend far beyond the flightdeck. Anyone who doesn't take that seriously is not fulfilling their obligations.