sounds like you are on your module 5 hypnotherapy assignment?
anyway, which relationships are being discussed? is it the relationship of treatment of these issues via hypnotherapy? is it the relationship between the issues themselves?
there are habits that can lead to stress, anxiety and phobias. the habit(s) that lead to these, tend to be excessive substance use. (narcotics, alcohol abuse etc.)
generally speaking, stress and anxiety have a direct link. if your are experiencing a form of stress in your life for a long enough period, and/or if the stress is acute enough, then you are more than likely going to encounter some form of anxiety as a result of that stress.
anxiety itself can ironically cause further stress.
phobias can cause stress, anxiety and habits. (mr z. suffers from arachnophobia, consequently, if in the presence of a spider, mr. z starts to feel his stress levels rising. his heart rate is increasing and he begins to perspire. he can feel the fear increasing and he is suffering a shortness of breath (anxiety). the adrenaline is rushing through him (fight or flight). as a result of this phobia)
to give a medical definition of each:
stress:
Forces from the outside world impinging on the individual. Stress is a normal part of life that can help us learn and grow. Conversely, stress can cause us significant problems.
anxiety:
a feeling of apprehension, uncertainty, and fear without apparent stimulus, associated with physiological changes (tachycardia, sweating, tremor, etc.).
Habit:
a behavior pattern acquired by frequent repetition or physiological exposure that shows itself in regularity or increased facility of performance OR an acquired mode of behavior that has become nearly or completely involuntary.
phobia:
An unreasonable sort of fear that can cause avoidance and panic. Phobias are a relatively common type of anxiety disorder.
hope this helps! and good luck with your essay.
PS. as for treatment, well there are many ways of treating these issues (CBT, psychotherapy, hypnotherapy, TFT etc. ) before treatment can commence, it is imperative that you find out the primary issue or in the case of a phobia, find the Initial Sensitising Event and address that first.