S.H.
It's a phase. Main thing is to not turn it into a control problem and then exacerbate his "fear." No need to "punish" him for it either... since he is not really doing anything "naughty" on purpose.
Give him a shower instead. That might be a good middle ground.
If he pees, it goes down the drain. No problem.
They can't always control their body functions in the bath... even if they do pee beforehand.
My kids like showers too. Both my kids at that age went through a "fear" of the bath. It passes.
Good luck,
Susan