code: public static Intent callPhone(String phoneNumber) {
          Intent intent = new Intent();
          intent.setAction(Intent.ACTION_CALL);
          intent.setData(Uri.parse("tel:" + phoneNumber));
          return intent;
      }
docs: Calls the entered phone number. Valid telephone numbers as defined in the IETF RFC 3966 are accepted.
  Valid examples include the following:
  tel:2125551212
  tel: (212) 555 1212
  
  Note: This requires your application to request the following permission in your manifest:
  <code>&lt;uses-permission android:name="android.permission.CALL_PHONE"/&gt;</code>
  
  @param phoneNumber Phone number