Hi C.,
I do think this is a phase that most children go through. My kid screamed and cried through most of his baths, and now that he's ten and showers on his own, he whines until he has to get in on his own!
That said, the only thing I'd add to the responses you've had so far is to expand on the reference someone has made to a bad tub experience. If your son has been given a bath by anyone other than you, perhaps something awful has happened during that bath and he's afraid of reliving that experience (beyond water too hot or too cold, I mean). That is the only thing I'd investigate, if there's a possibility of it.
If you're the only person who's bathed him, or you know (TRULY KNOW) that it's impossible for something like that to have happened, I'd follow the advice/suggestions you've received so far.