Lord Shiva worships the Shivalinga

Lord Shiva worships the Shivalinga

This depiction is a favourite shaivic imagery. 
It is extremely esoteric and full of spiritual meaning.
Why does Shivji sit behind his own shivalinga?
Because,in the most simple of words: He's committed to His own creation.
If you compare this to a modern day analogy, where during an election , the contender for head of state also goes to caste his vote, and , normally we note that he's up early, and one of the first to caste His own Ballot, leading by example..
The difference is that in Divinity, there is no election, no selection,and no contest. But a seeker must respect the Divine ideal He seeks,this can only happen if the Divine Itself upholds its foundations! So too, shivji respects what his own shaivism stands for, He is the first adherent, the first to vouch for the Shiva way.. He is His own first votary .He believes in His own manifesto, and stands by His principles.
He leads by example and from the front.Incidentally, the term Yoga, means "to conjoin with the Divine" and Shivji is also called Yogeshwar, the God of the Yogis which title further simplifies the point.
Aum Namah Shivaya.
(shail gulhati)