DD7 went through a stage of being frightened of the bath. I spent nine months giving her a sponge bath next to the tub whilst her older sister played with toys in the bath next to her.
Then a further three months, when she started to lean over the tub to play with the toys whilst standing next to the bath. Finally, after a year of sponge baths, she conceded to a shower instead of a bath. Then by putting the plug in during her showers, we slowly eased her back into having baths.
At 3yo she's still not keen on getting in the bath, but once in she is fine most of the time.