An expert on the subject of penises, dongs, woodies, willies, doodles, dicks, erections, Johnsons, stiffies, junk, and other assorted phallic objects. Also cocks.
A phallusmonger may or may not be desirous of such objects, but they must necessarily specialize in the knowledge of them or deal in their distribution. See urologist, or gay pimp.
Willy gazed awkwardly down at the floor.
"Doctor, I saw this girl a couple weeks ago, and I think she wasn't clean... I think I might have a problem with my-"
"I'm afraid I'm not qualified to help you in that department." said Doc Johnson. "Here's a referral to see the phallusmonger."
He handed John a slip referring him to one "Woodie U. Wan" in the urology department elsewhere in the hospital. Willy cringed. "Is this some kind of joke? Couldn't you just, y'know, give me some pills or something?"