Is it that you are truly being "phased out" or is it simply that life is changing the nature of your interactions? Is your friend purposely excluding your from activities, or is it that life is taking up more of their time so you are not spending as much time together?
If its simply that the time you typically spend together is decreasing, you may not be losing your friendship at all - it's just the demands of life are resulting in needing to adjust how much time you expect to spend interacting with your friend. She may still be your friend in spirit, but may not be able to devote as much attention as she used to.
That happens - when I was in high school, I'd spend all day, after school and weekends with my friends. Then we moved on to college and made new friends, but some of my high school friends I'd call or write and maybe would see on breaks and then catch up over summer. After graduation I joined new clubs, started working - met new people, new friendships - and had less time for some of my older friends due to lack of time and distance. When people started getting married, moving all over the country, having kids...all this takes up time.
My feelings of friendship toward them didn't change - if there would ever be a crisis and they call, I'd do what I could to help - but the time I could spend just "hanging out" became more difficult as it was just hard to coordinate all our schedules. I'm lucky to meet with some of my friends in the area once every couple months for lunch or dinner. Friends that live in different states I'll see once a year or every other year. We'll email occasionally or call - but we all understand we each have our own lives to live, but we still remain friends in thought and spirit.
So in your situation - is the friendship really "dying"? Are you really being "phased out"? Or is life just changing the nature of how you expect to maintain your friendship - do you simply need to accept that she just doesn't have the same amount of time to keep in touch? If so, simply be happy for her life opportunities, and take this opportunity to fill the openings in your life with some new experiences and meet some new people to hang out with. And this will give you new things to discuss with your friend when you do have the opportunity to meet up.