According to this explanation phobias are seen as a learnt behaviour. It is a 2 process theory (Hobart Mowrer) as it involves learning through:
classical conditioning (learn the phobia - acquisition)
operant conditioning (maintain it)
We associate something neutral with a negative experience that scares us. We then develop a phobia of the originally neutral stimulus. A neutral stimulus, if paired with a frightening event (the unconditioned stimulus) leads to a learnt association.
Evidence: Watson and Rayner conditioned Little Albert to fear white rats