An intense fear of walking is called Ambulophobia. It is a type of specific phobia which comes under the category of anxiety disorders in the DSM-V.

Someone suffering from it will experience extreme anxiety when exposed to walking.

One gets anxious on the mere thought of walking and if the anxiety worsens, can suffer from full-blown panic attacks.

Ambulophobia is closely associated with the fear of falling. This is because one who fears falling, will refuse to walk or move from a specific position he assumed to be safe for him.

The name originates from the Latin ‘ambul’ meaning walk and Greek word ‘phobos’ meaning fear.

More Info: optimistminds.com