I'm "in my own little world" 99% of the time and can't pull myself out.

Or so they say.

I'm 20 years old and I have created a different life for myself. It's all in my head, of course, but my day revolves around pretending to be someone else. She's the same age as me, but she has a completely different life. Her name is Phoebe. I have the whole thing planned out.

It's so hard when I have to deal with the real things (being myself). It's no fun! And it interferes with my "real life" too.

I also have a voice that comes to me and she talks to me when something goes wrong, and especially when I'm Phoebe. Last night she showed herself. She's funny and we get along well, but I'm so confused and worried.

I can see the allure in a fantasy life. The drawbacks are obvious though. There are no real people in a fantasy life. And the real body needs real care and sustenance.
What brings you back from the fantasy world?

is there any way you can limit it or adjust it? for example, i am with my imaginary friend while doing research and i use it to help me to focus, or to talk to it to remember things.
but i see that your case is different.. i'd say to limit the alter personality in some way or adjust it, and talk with a therapist about that recurring voice.

how long has this been going on?

I think you should tell a doctor about hearing voices. Hallucinations might indicate something serious and should be checked out. But otherwise, I'd say this about what you are doing. If you don't like the life you have, you are young enough to change that for the better. If you enjoy your life better as someone named Phoebe, go for it. Change your name to Phoebe, wear your hair the way a Phoebe would, dress the way a Phoebe would, train or educate yourself for a career that a Phoebe would have and enjoy the life you really want for yourself. Life isn't all about fun; I still have to pay taxes, but at your age you should be figuring out what it is you want to do in your real life, to make your real life enjoyable.

If what you are really saying is you like to playact; there is no reason why you can't do that for a living or a hobby, either. The way you have written your post, though, makes me think more of avoidant personality disorder, than of a budding actress. Make the authentic life you want and live it!

I've known men less than twice your age that would be thrilled to keep it up as long as you have...Lucky!

-Fleeing Bellocq, Muse of the Mission District