While on a call, tap Add call.
Enter the 10-digit phone number and tap the Call button.
To dial a number from the contacts list, tap the Contacts tab.
Note: If a Complete action using prompt appears, tap the preferred application, then tap to check or uncheck Use as default app as preferred. Once finished, tap OK.
Scroll to and tap the preferred contact.
Tap the preferred phone number.
After the second call is connected, tap Merge calls.
The conference call is now initiated.
Tap End to end the conference call.
Note: To end just the last call, tap End last call.
The conference call is now ended.