my 3 year old daughter has become very quiet nothing has happened at home i even asked her school teachers but they just said she is a quiet child that it is just a phase she must be going through any help on this many thanks

There's something definately wrong. Children don't go quiet for no reason. My partner's sister once virtually stopped talking for nearly a whole year, she sometimes would merely whisper. The whole family recall the distressed it caused and couldn't coax it out of her. She underwent many tests which revealed nothing. Eventually it turned out that she was scared of her maths teacher and the following year when her maths teacher changed she found her voice again!
If she continues with being quiet and you don't think it's normal behaviour then you must try and solve the root cause of the problem. If necessary seek professional help.