When you're in a call, you can conference in another staff member. Just follow the steps below.

On a desk phone

1. Tap the conference button, seen in the bottom left corner of the screenshot below
   
   
2. The list of call participants will appear. Tap the button in the lower right (person with a plus sign) to add a party to the call.
   
   
3. Once you've located the person, click the check mark button next to Add members to add them to the call. They'll appear in the call screen after answering the call.
   
   
4. When you're done adding people, tap the banner labeled Tap to return to call to return to the main screen.