To my knowledge you cannot determine the physical socket to which a display is connected. Please keep in mind that using DP 1.2 you could have multiple displays connected to the same physical socket as well.
The iDsiplayPhysicalIndex and iDisplayPhysicalAdapterIndex belong to the display. iDisplayLogicalAdapterIndex (which is part of ADLDisplayID as well) specifies the Adapter that belongs to this display.If you want to determine the iDsiplayPhysicalIndex of an adapter you can loop through the displays until you find the display with the matching iDisplayLogicalAdapterIndex.
Chris