Gabe got stuck in an elevator in a high-rise office building one morning. now he refuses to enter an elevator. if "entering an elevator" is the operant, what type of consequence has altered gabe's behavior?

The type of consequence that has altered Gabe's behavior is punishment by application.
Punishment by application is the term which is sometimes used to denote positive punishment. Positive punishment refers to an aversive stimulus that is added to a situation. In this case, Gabe feels aversion towards entering an elevator because he god stuck once.