There are a fair number of callers that will address him as Dr. Levin, not as many as there used to be, but I still hear one or two each week. I assume that those that do address him in this manner, do so out of respect. He never makes any bones about it either way.
He is a "colorful" character in some ways and most people either love him, or hate him. (I'm in the "love him" category.) Many of his callers will also address him as "The Great One" (hence the TGO references) as a slightly humorous sign of respect as well. (I'm not sure of the origin of the "The Great One" address, it may have originated from the mouth of Sean Hannity, and has stuck for many years.
Rush used to call him "FLEE" as in F. Lee Levin as a sign of humorous respect and collegiality.
Love him, or hate him, you have to acknowledge his dedication to conservative causes, his track record of walking the walk (see the many cases of his Landmark Legal Foundation), his prodigious knowledge of COTUS & SCOTUS and the philosophies that the Founders used as guidance and direction, and his willingness to speak the unvarnished truth about both sides of the political establishment, both the Rs and the Ds.