Taking a closer look, you can see that this Insect Spirit comes into play with 2 +1/+1 counters and also has Trample. The Trample really isn't as relevant as the fact that the Nantuko is actually sort of tough to kill. Each time Phantom Nantuko has damage dealt to it, you prevent that damage and remove a +1/+1 counter from it. The Nantuko also has the ability to add a +1/+1 counter to itself by tapping.
It's rather possible with enough untap shenanigans to make the Nantuko fairly large to the point that the Trample actually could become relevant. It's hardly the strongest card out there. But if you have a way to keep tapping it or get more counters onto it, then this Insect is pretty useful. It's also a Spirit, which means something to some people. Not that I'd ever try to build Spirit Tribal, but some have, especially around Kodama of the South Tree!
The Nantuko was a solid, if not great, reprint for the Commander product. Even today, Phantom Nantuko is featured in a handful of Derevi, Empyrial Tactician lists, hearkening back to the pre-constructed list. He's also made guest appearances in the decks of Ezuri, Claw of Progress, Ghave, Guru of Spores, Vorel of the Hull Clade, and Atraxa, Praetor's Voice.