Phase 3 is based on attention. You get a picture of your distractor, sometimes accompanied by a picture of what you are trying to be trained to be attracted to (your "target").
When you are paying attention to your target, you are allowed to stimulate yourself. If you are not paying attention to your target, then you can't stimulate yourself.
BUT, it doesn't matter where you are looking. USUALLY you look at what you are paying attention to and you pay attention to what you are looking at. But if you experiment right now, you will see that you can look at one thing and pay attention to something different.
So if you are looking at the target, but your attention shifts to the distractor, you have to stop touching yourself. Same thing, if you are looking at the distractor and your attention shifts to the target, you start stimulating yourself.
It also doesn't matter what you WANT to pay attention to. Suppose you want to pay attention to the target, so you can stimulate yourself. Fine, but if your attention shifts to the distractor, you have to stop stimulating yourself.
Phase 3 is a lot of work, but it develops a strong attraction to your target.
Explanation of Beginning Training
Explanation of Normal Training