No sound for incoming calls and outgoing calls on iPhone

If you're not hearing sound when someone calls you, you can try these steps:

• Check the mute button: Make sure the mute button on the call is off. 
• Check the volume: Make sure your phone's call volume is turned up. You can do this by pressing the volume rocker on the side of your phone or adjusting the volume in your phone's settings. 
• Check for obstructions: Make sure your phone's microphone or speaker aren't covered by a case, screen protector, or other objects. 
• Check your phone's mode: Make sure your phone isn't in Do Not Disturb or Airplane mode. 
• Restart your phone: Restarting your phone can help fix sound issues. 
• Check your signal strength: Poor signal strength at either end of the call can affect the sound quality. 
• Check your Bluetooth: Make sure Bluetooth is turned off. 
• Update your phone's software: Updating your phone's software can help fix sound issues. 
• Test a headset: Try using a headset to see if the other person can hear you. 

If you're still having trouble, your phone's speaker might need service. 

AlWeir did a good job explaining what to do, but to hear an incoming call do the following:

Settings > Sounds & Haptics > Ringtones and Alerts

When you get there set the slider to max, then turn Change With Buttons to off.