Phobia Support Group
A phobia (from the Greek "fear"), is a strong, persistent fear of situations, objects, activities, or persons. The main symptom of this disorder is the excessive, unreasonable desire to avoid the feared subject. When the fear is beyond one's control, or if the fear is interfering with daily life, then a diagnosis under one of the anxiety disorders can be made.

Have you tried therapy or do you have an idea of where this phobia could have come from? Like any traumatic experiences? Or is it something that's existed as long as you can remember? Have you tried touching the metal surfaces that have bothered you or do you completely avoid them? Do any friends/family members know about this?
The only strategy I can come up with is thinking of some metal surfaces that don't bother you (I'm assuming that texture is the biggest issue?), like your car, and give those a try and gradually move on to more textured ones. Or maybe look around for things made of metal that are "okay" for you and make a list of them, and make a list of the ones that stress you out and label those as "not okay" and continue looking around for metallic things and have the goal of making that "okay" side of the list bigger (if you want). And it'll be okay if you have more things on one the "not okay" side than the other, the list of things won't define you.
I'm no expert or psychologist - this is just my advice/ideas.
I wish you well, and I'm sure you can overcome this <3