Barrels are all preference, as are most things in paintball. If you want a quite barrel, get one with lost of ports, but remember you will lose air efficiency then. As said above, most of your accuracy comes from the quality of the paintball. One thing you are going to want to buy is this:
What it is is a detent kit. It works as a barrel kit...sort of. What you will find with your Phantom is that if you cock your marker, and hold it at a downward angle, your paintballs will tend to roll out of the end of the barrel. With this kit you find the ring that matches the size of the ball and you put it in following the instructions that will be given on the sheet of paper you receive. Then you won't have any more roll outs! They can be purchased at the site at the bottom of the picture. Go there, then put your mouse over "Gun Accessories" and click on the link labeled "Phantom Parts & Upgrades" the kit should be near the bottom of that page.