You'd need an (emulator)<http://www.ndsemulator.com/>] and the approriate [rom. Also, for it to be legal, you would have to own the game (as in, go and buy the cartridge, even if you won't actually use it). Honestly, I suggest just buying the DS, it's become quite cheap (unless you want to go for the 3DS, like a boss). It's also very fun to use, has awesome games, and is NIGH INDESTRUCTIBLE.

Oh, there's also a site that does fan-games of Phoenix Wright. They are quite good and carry the Original Flavor very well, at least those I tried,.

Problem is, most of them, being fanfics, can be SPOLERIFFIC. Be aware.