Quite simply, because it is the airline’s policy for her to do so.
There are certain types of electronics that can never be used on aircraft via FAA regulations (and that carry over into international airspace.) Boarding/Takeoff is one of the busiest and most “dangerous” times on an aircraft, so it is much easier to ask everyone to not use anything at all (or in the case of some airlines, to only use things that are easily identifiable) than to try to figure out whether or not something is allowed or not.
Originally Posted: https://www.quora.com/Why-air-hostess-asks-to-not-use-phone-while-plane-is-taking-off
Originally Posted On: 2015-12-28