How to beat a phobia?

First you should realize that the fear is based in the anticipation of the event. Your mind builds it up as being this big thing, long before you even see the building that holds the room that has the needle. You need to work to stop that wave from building power. Each time your mind starts to spin up, tell it no, you aren't going to spin up, you'll deal with it when the time comes. You will have to do that a lot, but the interrupting process is more important than actually not thinking about it.

Next, it would help to be able to work on selecting your field of attention. You're going to have to practice this, because the fear is strong, and will overpower your mental efforts on the day, so you need to practice this at least twice a day so that it will be familiar enough to your body, to happen easily (like muscle memory). Find 5 minutes in your morning and evening to sit still. Focus on a sense, like sound. Pick out a sound, and pay attention to it. Then try and pick out all the different sounds, try to find ones you might not have been aware was even there, but totally was the whole time. The sound of lights humming, breeze, your body shifting, birds, etc. No pick two sounds, and realize that they both hit your ear at the same time, and since sound is just frequencies your ears pick up, really both sounds are one thing as they hit your ear. Your mind separates them, but there is just one vibration hitting your eardrum. Notice how both is true, the sounds are separate, but they are the same. Try it with different sounds, and just sort of be a witness to this reality. The point of this is to build the muscle of awareness of choosing. You are always choosing things to notice, and things to ignore. It happens unconsciously, but you are making choices.

If a sound is annoying, this is good, because it is a chance to notice that you can only be annoyed by things you pay attention to. Things you aren't aware of can't bother you. You have to pay attention to something annoying, for it to be so. At first you won't be able to ignore something annoying, but by practicing, you will be able to merge that sound, with others, then focus back on the sound. Back and forth like flexing a muscle. It can have an effect similar to when you repeat a word so often that it starts to lose all meaning as a word, and just sound ridiculous to you.

The same with sight. Take a moment, and just notice all the things in your field of view. First objects, then color, texture, etc. What things did you not notice about what you are looking at initially. Why did you choose the things you did, what things did your brain ignore at first? Then, ask why things are separate. The picture on the wall is separate from the wall because we know that they are two things, but if you were an alien dropped into this moment without context of what a wall or a picture is, visually, it might just be a thing that is flat for a while, then changes color (shadow) and changes again. Sort of a difficult concept at first, but an easier way to get to it is by looking at negative space as a thing. If a door is open, you see the door, and the stuff beyond, but you don't often see the shape created by the space in the open door frame. What is the shape of the space between the arm of the chair and the seat? It's about looking at things that are in your field of vision, that you do not normally see. They are always there, but your mind chooses not to see them.

You can do the same with touch, feeling the sensation of your feet in your shoes, your legs pressing against the chair. Sensations you don't pay attention to normally, but are always there.

You can do one, or all three during a training.

Now, on the day, keep putting off your mind's desire to focus on the event, saying you will deal with it in the moment, and not before. At the moment of the needle, you can use one of those awareness techniques to become so distracted by something other, that your mental resources are all used up, and little is available for worrying about the needle. I wouldn't look at the needle, or the site, because that is just giving your mind something to focus on that can be unhelpful. Remember, that there is so much information in this moment to focus on, hundreds of sounds, sights, feelings, smells, and you have a small bandwidth to perceive just a fraction at a time. What fraction of the world are you choosing to see? Why not let the fear of the needle be a part of that huge amount that gets ignored? So much information gets ignored, no reason that the needle couldn't be part of all that, instead of the part that gets the focus.

You should keep this in mind that needles do hurt but for a very brief moment. It will be over before you know. Intead of stressing over it persistently, its better not to think about it and keep your attention focused on some thing else