From the side menu bar, click Contacts > Contact List
Click "Filters" and then select "Category" IS and choose your category or categories for the last box. Click "Search."
Next, to select all contacts on the page, check the box next to Name.
In the Bulk Actions box, select the phone icon to add these contacts to your call list.
When the Add Call modal pops up, you can fill out the reason for contact, call type, and the date you'd like to schedule the call for. Then click "Save"