Here are a couple of things to check to start with.
1. Verify your mute is off. Maybe something caught the switch.
2. Check the volume on your phone. Maybe it's lower than you thought you was.
3. If you use any Bluetooth speakers of any kind, verify your phone is not connected to them and trying to play sound out of them.
4. If everything else is verified and you still are not hearing the shutter sound then first force the camera app. Double click the home button and swipe up on the camera app.
5. If all else is verified and after force closing the camera app the shutter sound still is not there then hard reset your phone. Hold down the power and home buttons until the Apple logo appears.
6. Of all else is verified, force closing the camera app, and hard resetting your phone did not restore your shutter sound. Make a Genius Bar appointment if you have an Apple Store nearby.