While on a call, tap the Menu icon.
Tap Add call.
Enter the 10-digit phone number and tap Call.
To dial a number from the contacts list, swipe left to the PEOPLE tab.
Scroll to and tap the preferred contact.
Tap the preferred call number.
After the second call is connected, tap the Merge Calls icon.
Tap END CALL to end the conference call.
The conference call is now complete.