Phobias mean here which you always avoided as much as you can. You can say that phobia is Something happens very early in your life that you saw the particular thing and it affected you psychologically. This is stored in your mind which is the moon in Vedic astrology. You have to look where your moon is placed in your birth chart and which nachhtra is in. Whatever the purity and impurity of nachhtra are like what is that nachhtra like and dislikes. And if your phobia gives you panic attack and so much fear then mercury is involved with the moon. You have to analyze the second house of your birth chart because the second house represents that your environment the things near you that you are experiencing. Find out what your second house shows. Mercury represents your nervous system in Vedic astrology. So if phobia converts into attack you need to look where your mercury is placed and which nachhtra is in.