As of version 15, the recording controls are found in the Phone Provisioning screen of the 3CX Web Admin.
Select "Extensions" from the left menu and then "Edit" your extension. Select the "Phone Provisioning" tab and then Select the "3CX Client" from the "Your Phones" area. You will find a section titled "Access" in that section there is a "Show Call Recordings" option. Make sure this is selected.
Find out more about 3CX Phone System at: http://www.Office-Phone-Systems.ca