Shyness can be a form of social phobia. It basically becomes a social phobia when it interferes with normal everyday actions and your ability to function in society.

If you're in a group and your mind occasionally wonders to what others are thinking of you, that is more just being shy.

If you are at places and you can't get your mind off how others are looking at you and what they may be thinking of you, then that is a mild to moderate form of social phobia.

If you completely avoid places for fear that they will look at you or are woried what they may think of you, that is usually a moderate to severe form of social anxiety.

Hope that helps some