Agoraphobia is a very complex phobia. It usually manifests as a collection of inter-linked phobias. For example, many agoraphobics fear being left alone (monophobia), dislike being in any situation where they feel trapped (exhibiting claustrophobia type tendencies), and fear travel away from their "safe" place, usually home.
Some agoraphobics find they can travel more easily if they have a trusted friend or family member accompany them. However, this can quickly lead to dependency on that companion. The severity of agoraphobia varies enormously between sufferers from those who are housebound, even room-bound, to those who can travel specific distances within a defined boundary.