Gladys Hill, for years John Huston's personal assistant and co-writer, contributed greatly to the preparation of the final shooting script for Phobia uncredited. She was given a credit as "assistant to Mr. Huston".
Melvyn Hill (no relation to Gladys) was also a major contributor to the development of the script. Professor Hill, a psychologist whose knowledge about the criminally insane as well as his credible creative writing skills also advised Mr. Huston with the preparation of the script. Uncredited.