Oh geez, that's a big question with a lot of answers.

There's a lot of great classic Phish out there, but as they're still making music now, I'd say it makes sense to fall in love with current Phish. Get to know the band as it exists, save the older stuff for later. But whatever, it's all good. :)

For recent stuff, Magnaball was off the chain. It's a three day festival. If you like far out trippy shit, make sure to watch the "secret set". Most of summer '15 was the best Phish of this era. The shows they just played at Dick's in September '16 were really good, too. These should all have professional quality video out there somewhere.

I'm sure people will come in here with their pet favourites from the 90s. If you're keen on just audio, Spotify has a lot of their older shows released as box sets. Roxy '93 is a great run. The Island Tour is a pivotal Phish moment. NYE 1995 gets a lot of love. Amsterdam 97/98 is another good one.

You can also check out LivePhish for a variety of shows. Their "plus" subscription gives you streaming access to every show since 2002, a shit ton of older stuff, side projects, albums, etc.

Welcome! It's a good time to be a fan. They're a fun band.