[xamarin form]]Well in native android you have the telephony manager to check what is the state of your device > APP Dev

https://stackoverflow.com/questions/52386242/xamarin-forms-how-to-know-when-a-call-is-currently-taking-place

Well in native android you have the telephony manager to check what is the state of your device:

It has three states:

• Idle: when it's idle there is no call
• Offhook: when Off-hook it is in call

• Ringing: when Ringing

      var telephonyManagerService = (TelephonyManager)Xamarin.Forms.Forms.Context.GetSystemService(TelephonyService);
      var getCurrentState = telephonyManagerService?.CallState;
      switch (getCurrentState)
      {
          case CallState.Idle:
            //No call
              break;
          case CallState.Ringing:
            //Ringing 
              break;
          case CallState.Offhook:
            //On call
              break;
          default:
              break;
      }