Phobia is a type of anxiety disorder,
more than a simple fear of an object, animal, place or situation.
Anxiety can exhibit in different forms and levels of intensity, ranging from slight sense of uneasiness to a full blown panic attack depending on the severity of your phobia. Regardless of the level of intensity, it affects the person psychologically, physiologically and behaviourally. 
 Traditionally, actual exposure to fear is the most common solution, but as research studies have shown, exposure in vitro can be just as effective.
Hypnotherapy can be used as a type of virtual reality treatment to overcome the potential dangers of real life exposure and to create a safer environment where the individual can be guided in vitro (in their mind) through the imagined gradual exposure. 
Hypnosis is effective in vivifying the mental imagery involving all senses, for increased focused attention and effective in preparation to in vivo (live)exposure through the dissociative nature of the treatments such as rewind technique. Desensitisation with relaxation in hypnosis involves increasing the tolerance to fear in small associated steps while remaining in a calm and relaxed state.
 

WHAT IS PHOBIA?

There are two biological and evolutionary fears that we are all born with: a fear of falling and fear of loud noises.
Phobias are born when a person begins to organise their life around avoiding the thing that they are afraid of. 
Phobias are psychological and a learned response in the brain and can be defined as a fear of a fear, an extreme reaction to fear triggered by a stimulus or a one time faulty learning.
They are very common: in UK alone 10 million people have a phobia (NHS Choices 2012). Estimates of the proportion of people who are likely to experience a specific anxiety disorder during their lifetime are 12.5% for specific phobias compared to 4-10% for major depression.
Types of phobias:
There are many known single phobias, such as acrophobia, agoraphobia, anthrophobia, achlophobia, aquaphobia, astraphobia, aviaphobia, bacteriaphobia, prontophobia, claustrophobia, hematophobia, glossophobia, mysophobia, nomophobia, ophidiophobia, panaphobia, xenophobia, zoophobia and so on, however they can be divided into two main cathegories:

Simple Phobias – fears about specific objects, animals, situations or activities, such as:

Dogs, spiders, snakes, enclosed spaces, doctor or dentists, flying, heights etc
Simple phobias usually start during early childhood and often disapper on their own as the child gets older.

Complex Phobias

Complex phobias tend to be more disabling than simple phobias as they are often associated with deep-rooted fear or anxiety, such as with agoraphobia or social phobia.
Complex phobias usually start later in life. Although the exact causes of complex phobias are ofen unknown, it is thought that genetics, brain chemistry and life expererience may all play a part.

SYMPTOMS OF PHOBIA

All phobias affect the person psychologically, physiologically and behaviorally. They can limit your daily life, personally and professionally and may cause severe anxiety and depression.
 
People with phobia typically have a need of avoiding contact with their source of fear and anxiety and may develop strategies to support their need. For instance, someone with a fear of dogs may not want to touch one, or even look at a picture of one.They may actively avoid a park where dog owners take their pets for a walk.

Although all phobias share common symptoms such as anxiety, they also exhibit different symptoms and triggers:

Simple phobia (such as specific phobia) typically includes a strong fear and avoidance of a particular type of object or situation (such as dogs).

Acrophobia (fear of hights) for example differs from agoraphobia (fear of open spaces) in that the sufferer does not experience spontaneous panic attacks or a fear of having a panic attack. And both of these for example also do not present a fear of humiliation or embarrassment in social situations common to, for example, a social phobia.

Complex phobias, such as agoraphobia and social phobia tend to be more disabling than simple phobias as they are often associated with deep-rooted fear or anxiety. Agoraphobia, for instance, may involve several interlinked phobias, such as monophobia (fear of being left alone) as well as claustrophobia (fear enclosed spaces -fear of feeling of being trapped).

As well as feelings of anxiety, people with phobias may experience panic attacks.
 
The physical symptoms of  a panic attack can include:
 
sweating, trembling, hot flushes, chills, shortness of breath, rapid heartbeat, chest pain etc.
 
Phychological symptoms may incude:
fear of losing control, fear of fainting, feelings of dread, fear of dying.
 
Read more on symptoms on  Anxiety Disorders