Cosmic- I'm not going to say don't go to the urologist, it's your call. I wouldn't bother if the antibiotics are doing the trick. Save yourself the copay. If you have a good relationship with the ped who sees him regularly- in a few years if the ped still thinks the foreskin might be tight- maybe then think about treatments for that (conservative ones) but really I would not even begin to be concerned till a boy is about 5... and even then- it's not like surgery would be in order.
I am just confused about the diagnosis you got- because phimosis has nothing to do with an infection- I mean you can have phimosis and have an infection, just like you can have a cold and have a big nose. But "big nose" does not mean "has cold".
As for how you have been treating him- I don't think you need to change a thing- not the way you have been caring for him- not the diapers, not the ointments- nothing! You have been doing everything right! this was just a fluke! Diaper ointments are ok if he has a rash or if his skin seems irritated- if he get's sick- diahrea (sp?) can scald skin and a barrier ointment might be good. If you nurse and get thrush, if he gets diaper yeast- his foreskin can get yeast (watch for this now with the antibiotics) and OTC yeast meds can work for that.
Urine is sterile and every time he pees the inside of the prepuce opening is flushed OUT. If you try to scrub into there- you will push contamination IN. Let the urine flowing OUT do the job of rinsing out the lining. This part of the body is designed for contact with urine and you do not need to wash the urine off it any more than you would need to scrub out your uretrha after taking a pee. The urine is fine.
As for what you saw- I do not doubt that his foreskin looked AWFUL, but if it is any consolation- try to remember that the foreskin is a very loose fold of two layers of skin, so there is a lot of room for swelling. If you hit your wrist with a hammer- it might swell a little, but the skin itself is tight enough that it has it's own hugging potential, it's not going to just swell and swell. But imagine another place on the body that does not have a bone under it- your LIP- have you ever had a fat lip? You know how fast it can swell up? And also how soon the swelling goes back down? Or the eyelids of a beat up boxer? Or an allergic reaction that someone might have in their eyes? That's because there is room for the swelling to happen. Foreskin injury/infection tends to LOOK a lot worse than it actually is because of the double layer loose swelling. Try to not apply the same scale of "drama" (I can't think of what else to call it) to the scene you saw as if you saw this elsewhere on your son's body. I know it looked bad, but it was probably just "fat lip" type reaction.