Final answer:
According to Freudian psychology, failure to properly progress through developmental stages can lead to psychological issues in adulthood, such as phobias, making Sigmund Freud the psychologist who best fits the description of the theory mentioned.
Step-by-step explanation:
The question seems to be asking which psychologist had a theory that would explain that a person, in this case named Phoebe, has not achieved their full potential and as a result has developed an anxiety disorder such as a phobia. Among the listed options, Sigmund Freud is the psychologist whose ideas relate most closely to individual psychological development and the formation of anxiety disorders as a result of unresolved unconscious conflicts, particularly those rooted in childhood.
Freudian psychology posits that failure to properly engage in or disengage from a developmental stage results in emotional and psychological consequences throughout adulthood, potentially leading to phobias. For example, Freud's case study 'Analysis of a Phobia in a Five-Year-Old Boy' illustrates his ideas regarding the unconscious and the development of phobias.