A Call Action is one that, when tapped, automatically initiates a call from the user's smartphone to a telephone number you designate.
Create a Call Action
Enter the destination telephone number to create a Call Action.
Or choose the "Pull from Data Tab" option, and the Action will get the phone number from the app's database, located in the Data tab.
Reference the Action Formatting and Controls FAQ for a refresher on the controls that are common to Actions.