You'll need a cable with XLR connectors. This allows better protection from interference than a minijack you'll find on some cameras. There are a number of manufacturers to choose from. The length of the cable will be determined by what you use the mic for. If it's sit-down interviews, you might get away with a 25 foot cable. You might need more if you are moving the boom and recorder while talent is walking around. The 25' cable is what I use most often.
Phantom power is power supplied by the recorder or other device to power a condenser microphone. It powers the electronic circuitry in the microphone, and is rated at 48 volts.
Minor correction. Phantom has no required level. It's most commonly at 48V on professional equipment and some microphones require 48V to work properly (most will work at 15V). But 15V and 12V are also fairly common on consumer gear so it's something you want to look at the specs at before you buy to avoid surprises.
I'm pretty sure the H4n is 48V (or close) and depending on which NTG microphone you have you may not even need phantom.