Phoenix was my first attempt at doing an orchestral soundtrack. I had already done some 'half orchestral' stuff before, but I hadn't gone all the way like this. I bought some sample-CDs with orchestral sounds on it (Peter Siedlaczek's 'Advanced Orchestra') and spent about a week just sampling instruments and mapping them out in the synths. There are literally thousands of samples involved, because all instruments are 'multi-sampled' on every 3 half-notes up and down the keyboard.
I then spent a bit of time researching some basic orchestration, and when I mapped all the samples out in the synthesizer, I was able to position each instrument more or less correctly in the stereo field. I also considered the distance from the close audience to each of the instruments, and applied more reverb to the instruments that are further from the listener, and less reverb on the closer instruments, to try to make it sound a bit more realistic.