Step 1: Obtain 2 calls:
To conference call you must have 2 calls on the phone. One that you are speaking with and one on hold. Lets say you are already on the phone with the 1st call.
There are 2 ways get the second call:
a) Receive the 2nd call: when you are on the phone with one call and a second caller is calling in, you will see this call on the LCD as well as hear a beep and the phone will give you the option to get the 2nd call. One of the soft keys will say "answer" press this soft key. This will put the other call on hold.
b) Make the 2nd call: You are on the phone with the 1st call. Press the hold button, then press "new Call" then dial the new call and press send.
Step 2: Join the calls.
If you have 2 separate calls on on the phone at one time you can join them. One of the soft keys (buttons below the LCD) will appear with a label of "Conf" You can hit this button to join the calls into a conference call.
If you are on a call and want to call another person to conference in, hit the "conf" button. It is a soft key that is directly under the LCD screen, usually the 3rd one from the left on most Yealink Phones.