Here's the thing: If you shoot a picture of yourself from below, all you're going to get is a very up close and personal view of your nostrils, double-chin-that-doesn't-exist-anywhere-but-this-angle, and droopy eyelids. Just don't do it. (Too close, too high, too low.) Unless you're trying to make yourself look like an alien, it's worth framing yourself correctly when taking selfies.
Hold your arm with phone in it out in front of your chest, so that you're making a 90-degree angle between your torso and arm. Move it about 15 degrees to the side, and up about 5-10 degrees. There you go.