Hello kajsiR,
Welcome to Apple Support Communities. From what I understanding is you're hearing a crackling sound from the speaker or nothing on phone calls. The callers on the other side are hearing the same issue. When using only functions as FaceTime, Facebook Messenger calling and other internet calling platforms everything is working normal, correct? I'm here to help you take a look in to that!
Before looking into additional troubleshooting steps to isolate if it is a software, hardware or environment issue. Many I ask a couple questions?
- Have you test the SIM card in a different device?
- When on phone calls are you using speakerphone or placing the iPhone to your ear? Speakerphone and FaceTime will use the front microphone, when phone calls will use the bottom microphone. Be sure nothing is covering the bottom microphone.
Here are a couple articles I would suggest to read over on software troubleshooting steps:
If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker
If you see No Service or Searching on your iPhone or iPad
Before going into software troubleshooting, a backup of the data on the device would be encouraged to iCloud or iTunes:
How to back up your iPhone, iPad, and iPod touch
If the issue persists, please don't hesitate to post a reply!
Cheers!
