I'm glad it worked. I discovered it by accident when I decided to see how well the Pheonix would fire. I noticed that if the target was way below me, it would detonate prematurely. I know that in this sim, ground clutter can sort of mess-up with radar tracking, so I thought the same thing applied to the Pheonix. Good guess on my part.
Just another tip, if you know your target is flying around a mountainous area, or that there is a mountain between you and him, and if he is above the mountain, the minute he dives behind it, the missile will lose lock. Unfortunatley, in this scenario, you have to use shorter range weapons and fly low and fast to baffle the other guy's radar.
In short range engaments, such as where you're chasing the target around minimum range of the Pheonix, you can still succesfully use the pheonix to destroy the target, but it takes patience and timing. If the target is turning one direction, just wait for him to begin turning the other direction. The minute you notice that happening, point your aircraft to the guestimated point of impact with the missile and the target and fire the Pheonix. The target will either begin to turn back the direction it was originally going in an attempt to evade the missile (doing this only delays him/her there around that area of impact, allowing the missile an easier chance in maneuvering to hit the target) or the target doesn't turn the opposite direction and continues on it's new course of direction. While doing this, the target still has to deal with the inertia and momentum to begin traveling on it's new course of direction, in which you have already setup for the missile to travel. Essentially, the missile sort of becomes a rocket without any real need, or at the very least, minimum need to maneuver. Considering the speed of the pheonix when launched, it is a no win situation for the target. It is doomed.