The best Phish is live Phish, the second best is recorded live Phish. I definitely recommend seeing them in concert at least once, but until then the there are a couple ways of procuring live Phish recordings. The first would is the time honored tradition of bootleg CDs or tapes. The great thing about bootlegs is that Phish(and many other bands) actively support the taping of their concerts, even giving select seats in the middle of the area to tapers so they can have the best stereo imaging, another good thing is the cost, as it is actually against tapers edicate to charge for recordings so if you find somebody who has them you should be able to get a copy for a blank CD.
If you don't know anybody who has bootlegs, the internet has made it extremely easy to pass around recordings,
furthur is a file sharing program dedicated to spreading live concert recordings, unfortunately because of people sharing live Phish that Phish sells, Furthur has taken the ability to search for Phish out of the program
The best way in my opinion to get live Phish is to get one of the many live albums that Phish has released. The first is Hampton Comes Alive which is 3 nights(6 disks) of live Phish goodness or the the
live albums that Phish has been releasing of select concerts. The problem with most taped bootlegs is that the quality is ok - good at best. The live albums that Phish have released are Soundboard mixes which means the the recording device was plugged directly into the mixing board instead of picking up the sound with microphones. While Phish lets phans do soundboard recordings occasionally, I have not heard a better mix than the ones that are sold at Live Phish, the Hampton comes Alive mix is pretty good, but it really doesn't hold up to the most recent ones.