E., I am sorry you are going through this, but it is not just a phase. You need to find some answers, now. My niece was very much this way. It started at about age 3 and she is now 9. It has been a long row to hoe, but things are much better now. She would be fine and less than a minute later she was out of control. Very quickly, I discovered that she knew who would let her get away with it. It turns out she had anxiety and anger management problems and she knew how to use it. My husband and I begged them to not tolerate this behavior, but they did. Soon, we were the only ones that could keep her, because she did not do this with us. However, when her parents were around she did even though we were there. (My point is be firm, caring but firm.) These are the steps I followed and have really worked wonders with her. Although, I do reccomend counsiling, as I did with my niece, but she was not taken on a steady basis, so I don't know that it did any good.
Step 1 - Let them know this kind of behavior is not acceptable and you will NOT tolerate it. Be consistant.
Step 2 - Be supportive but firm. (I explained that I knew it must be awful to feel that mad, but that I still expect to be respected.)
Step 3 - Give him another outlet. If he feels like he needs to hit, give him a punching bag and explain that this is the ONLY thing he is allowed to hit. (We eventually got away from hitting all together, but it was a starting point.)Explain that there is no punishment for hitting the bag, but if he hits anything else or anyone that he will be in trouble. (We also established some ground rules such as even if she is not hitting she is not aloud to scream and rant all over the house. She must go to her room and calm herself down.)
Step 4 - Give him time to calm down. (My niece would try to get away to calm down and they would chase her around still discussing the problem. As adults, sometimes we just have to walk away. Give them the oppurtunity, as well. They do have emotions, and my nieces were raging out of control.)
Step 5 - Don't lose it. When he gets out of control, don't lose your cool. (This is the hardest part, because you have to stay until you get the point across. I would be 20 minutes, redirecting her, before she would start to calm herself, when we first started. I would have to say things like, "I know you are mad but that is not an excuse to disrepect me or be mean to me." or "Would you like it if I screamed at you or hit you? Then don't do it to me. I don't like it either." She would scream for me to leave her alone and I would tell her that as soon as she stopped screaming and hitting I would leave her alone for a while and let her calm down and then we could talk. ( I found it was important to let her know that a fit would not get her out of the situation all together.)
I am no therapist so I can't say this will definately work, but it did with my niece. I also not against spankings but in this case it did not make since to do that. Your son may not have this same problem but it sounds very familiar to me. I wish you the best of luck. God Bless.