To initiate a conference call:

STEP 1 Press the Conf button during an active call. The first call is placed on hold, a second line is opened, and you hear a dial tone. 
STEP 2 Dial the second person’s telephone number. 
STEP 3 Press the Conf button again. All three parties are connected in the conference call. 
When you hang up, the other two parties are disconnected. To keep the other parties in a call, but disconnect yourself from the call, press Join.

To conference two active calls on your phone:

STEP 1 On one of the active calls, press ConfLx. If you have two active lines, the calls are conferenced. If you have more than two active lines, you must scroll to choose the line you want to conference in.
STEP 2 Press Select.