Biological therapies operate on the basis that phobic disorders have a physical cause, and thus phobic disorders are treated in a similar way to physical illnesses.
One type of biological therapy is chemotherapy. Chemotherapy works on the basis that a chemical imbalance is the cause of the phobic disorder and so drugs are used to readress these imbalances.
Another type of biological therapy is brain surgery. This treatment assumes that phobic disorders are due to an area of the brain malfunctioning, and so the connections to this area are severed to "functionally" remove the area.