To charlie overcome his phobia of heights, his therapist trains him to relax and then has him imagine climbing a ladder. after charlie visualizes climbing a ladder without anxiety, he attempts to imagine standing at the top of a tall building without feeling anxious. charlie's therapist is using a technique known as

Charlie's therapist is using a technique known as CBT Cognitive Behavioral Therapy.

Explanation:

Cognitive Behavioral tecnique is often used to treat phobias, among other emotional or psychological afections. This tecnique is based on how negative emotionds and thoughts can be shaped into possitive ones, and so this can help deal with phobias or ansiety.

What Charlie's therapyst is doing is helping him relate his fear of hights with something nice and relaxing, that is how according to this tecnique people can overcome his fears by changing the idea of hights as a bad thing.

This tecnique works under the premise that behvior can be shifted with cognitive influence, this theory helps change thoughts that influence fear.