One way or another you HAVE TO get over your doctor phobia. Like the rest of us, you'll have to see the doctor now and then, and it could be a case of life or death, sooner or later. Don't waste any more time being a victim of this phobia. Take action - whatever action you think will help (difficult to advise what will help you since a phobia is so personalised).
As a starter, you could try visualising the visit, going through it in detail in your mind, making it as real as you possibly can, and coping with it easily (yes, you can, in your imagination!). If you do this time after time you might be surprised how quickly the whole thing starts to lose its dread. Also, make the doctor figure (whether it's someone you know, or just 'a doctor') a vaguely ridiculous character, someone you find funny, odd, pathetic, weird or in some other way harmless. This'll take the 'sting' out of your imaginings. I hope this helps.