Um...Here's how below, but I want to caution that you really need to be extremely comfortable with manual mode flight, and carry a lot of height and momentum to pull it off. It's very easy to crash in manual without doing flips, and you can do some serious damage to your phantom if you mess up the controls/timing.
First, get some altitude. Like 100ft up. Drop the throttle to 0, at the same time pull full cyclic in the direction you want to flip, either right, left, front or back. It'll start to flip. I find it easier if I initiate at the apex of an ascent. As it starts to come around past 180, bring the throttle back up to recover hover/altitude, and reverse the cyclic to regain attitude.
The best way to practice this is topic the phantom away and get a mini multi, like a nano QX, which you can crash repeatedly without damage.