Slashers. We had huge titles like Friday The 13th but then we also had the really nasty, violent ones like Maniac and The Prowler. Don't Answer The Phone holds the same tone as movies like Maniac with its level of realistic depravity.
Fans of "Don't!" movies such as Don't Go In The Basement, Don't Go In The Woods, Don't Open Till Christmas etc. should really add Don't Answer The Phone to their collection its a true sickie from the most vile year of the Slasher genre.