How are you defining "phobia?" If you are startled or disgusted by flies then that is not really a phobia. If you see a fly and run out the room screaming and have to lock yourself in the bathroom until the fly is gone, then that is a phobia - and no that is not normal.
Please be careful how you use the term phobia. Phobias are severe psychological illnesses that leave their victims suffering. To use the term lightly is offensive to those who suffer from a real phobia.