Real people don't have a facade of everything being "great" all the time, and they don't always appear to "have it all together." Real, genuine people let their "warts" and quirks show.
Phony people are often trying to show off. They always (only) talk about their successes. They tend to name-drop a lot. They tend to be overly assertive and act like they think they are "God's gift to the world", as if they have everything to offer you, but you have nothing to offer them. Very arrogant. Basically, they act like politicians.
Real people do sometimes talk about their successes, try to look good, and even name-drop. But you have to consider how much and why people do this. If someone doesn't let you see their "bad side", s/he is phony. Someone who is real will let you see all their sides - the good, the bad, and the ugly.
People are different, however, in how quickly they let you in to see all these sides. Quiet/private "real" people can be hard to figure out. They might appear phony at first because they find it hard to let people in to see the less good stuff about them, but it's not because they are trying to be fake. Here is where you have to consider a person's attitude. A humble person is real.