Here is a good article on describing the phases of play. For those of you who are not familiar with this concept, you could think of it as a "mindset" of a youth player in soccer. Although, most of us mistakenly think of the "phases of play" in terms of position such as "Defender" or "Scorer". We tend to think of that since a lot of us watch or have participated in different sports.
Here, we have to break that "thinking" in terms of every player.
When you have the ball, "everyone is attacking". When you don't have the ball "everyone is defending". However, depending as to where you are at on the field, do you as a player (or coach) able to recognize the "Principles of Play". (see AYSO U12 Coach Manual).