Yes it's a phase, and hopefully for you won't last too long. LoL My son is 3 right now and we're going thru the hair washing thing too.
My daughter was worse.. at 2 and half she suddenly became TERRIFIED of monsters in the bathtub and refused to bathe for about 2 months. I was pregnant at the time and exhausted so I just did the sponge bath thing for a while until it got to the point of her really really needing a REAL bath.. she screamed and we got thru it and it was horrible but finally she realized there were no monsters in the bathtub and mommy was right there and she would be fine. :::whew:::
They do outgrow it, I promise!! LoL I just tried not to associate anything negative with bathtime during that phase, never use bath as a punishment, try to make it fun with toys and bath crayons (the kind they can write on the walls with and they wash right off,,, I used Magic Erasers after the bath and it came off fine), and it eventually passes.
Good luck!!!