OS 9.3.1

You can try the following troubleshooting steps to fix the problem:

-Go to Settings and ensure the Do Not Disturb feature is not activated. Also check the volume on the ringer.

-Ensure the mute button is not turned on. Your iPhone could be silenced in mute mode. Flick the Mute button on and off several times to correct the problem.

-Go to Settings > General > Reset and then choose to Reset Network Settings.

-Hold the home and lock button together for few seconds until the iPhone restarts itself.

-Finally, go to Notifications and disable notifications for messages. Power off your phone and turn it on again.

Go to Setting > General > Reset > Reset All Settings

This will Fix your Issue caused by Update

Before you do that -

Backup the device to iTunes

Then restore to factory settings

See if sound works - this eliminates any software issues

If the problem resolves - restore backup

If it does not - then likely a hardware issue in which case

Please make a Genius appointment at an Apple Store, or go to another authorized service provider.

Check the ringer volume level and see if it is at 0.

If you can't hear a person on a call or voicemail or if the sound isn't clear on your iPhone - Apple Support.

If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker - Apple Support