ok a crossover (X-over) alows you to select basicly what kind of speakers you are going to be running with this amp for subs you would switch it to LP (Low Pass) this blocks frequencies of around 240 hertz and up if you were going to be running your component speakers with this amp then you would switch it to HP (High Pass) this well block frequencies of around 240 and below now as for phase shift i can only take a guess and that is it switches your polarity (switches - to + and + to -) please any one correct me if im wrong