World's Smallest Penis Undergoes Successful Growth Procedure

Michael Phillips -- the man who claims to have the world's smallest penis -- may soon have to vacate his teeny-tiny title ... because he says a procedure to give him some size was a HUGE success.

The viral sensation tells TMZ ... he went forward with his penis procedure -- which involved the injection of semi-permanent dermal filler into his member to increase girth -- at a hospital in North Carolina on Monday.

Michael says the visit was about 3 hours long ... explaining they took him into a room, prepped him with numbing cream and a numbing shot, explained the procedure, and proceeded to give him several injections of the filler on all sides of his penis.

Usually when he's flaccid, Michael says his willy rolls up and goes inside him like a hidden belly button ... but now it stays out -- and has made urinating far more comfortable.

Michael says there's some swelling of his private area which will last about a week or so ... and, when the swelling finally goes down, he'll be able to see the final result. As you can imagine, a few injections to the penis are quite painful -- but Michael says he considers the procedure a success.

He adds he hopes the size lasts ... and he says doctors told him he can come back in 6 months and repeat the procedure to add even more to his size -- or to maintain his new size if the dermal filler dissolves fast.

He reiterates this procedure -- which ran him $4K -- wasn't for a sexual purpose ... he took the shots to his shaft purely for urinating comfort. He was able to raise the money for the procedure via GoFundMe ... and he's still got plenty of extra cash for a second round.

Remember ... Michael -- who claimed his erect penis is just .38 inches -- planned on getting surgery at one point to increase his size -- but opted out over the potential risks.