Solution
Check your iPhone's ringer switch and make sure it is not turned to silent mode to prevent wasting time going through a number of troubleshooting steps. If you don't hear any sound from your iPhone's speaker for incoming calls or other audio functions, do this.
The ringer switch on your iPhone is placed on the top left side. Try flipping the switch on and off to activate Silent mode. The sound is turned off and the switch is in the red position if it is switched to silent mode. Just be sure to change the ring.
If the switch appears to be stuck, consider removing the case to ensure that nothing is blocking the switch.