See the video demonstration here.
D2, D3 and D4 are all LOW in this mode of operation. So no connection between these pins and the 3.3V pin.
In this mode the backlight on the target phone, the one you have attached the LDR to, must remain ON for between 20 and 40 seconds to turn the socket ON.
To turn the socket OFF the backlight must remain ON for under 20 seconds. You need to count the number of rings on the phone you are calling from in order to achieve these backlight timings.
For instance when I ring my target phone with my phone, the backlight with stay ON for 21 seconds with 5 rings. Therefore in order to turn the socket ON, I need to make 6 rings. To turn the socket OFF I need to make under 5 rings.
To Turn ON Socket: Ensure backlight stays ON for more than 20 seconds but under 40 seconds.
To Turn OFF Socket: Ensure backlight stays on for under 20 seconds.
Note that it will take 20 seconds to turn the socket ON or OFF.