I dropped my phone in water, sound won't come out when talking on the phone

I guess your definition of 'working perfect' is different from that of most people.

What's wrong is that it's been damaged by exposure of the electronics to liquid.

Make an appointment at the genius bar and get an out of warranty replacement. Sooner or later, the corrosion that started when it got water inside it will cause it to fail completely.

It isn't working perfectly if something on it doesn't work. If you turned it on while it was wet you probably did more damage than the initial soaking did. Your best option is to dry it completely (like for a week) before attempting to use it again. But even that isn't a guarantee that it will work right again. If you take it to Apple they will replace it at a heavily discounted price, as long as you don't try to fix it yourself (or have someone else try to fix it).