That's the only thing he does well. From what I've read and seen about Phelps, he's barely done a lick of work in his entire life. He's a carney, a con man.
And I really would know if Phelps' "monument" really exists. Phelps is known for telling a city/place he's showing up, stirs up the place--then not showing up. It'd be consistent with him to say he's got a "granite monument" ready to be placed in Casper, when this monument never existed at all. He's just stirring up Casper and they're falling into his trap. I just can't imagine Phelps actually spending any money on anything--except himself.