This is the characteristic of Phoenix ESC itself. You need to connect the Phoenix ESC to the computer to set the speed. By default, the Phoenix ESC has only two states: completely stopped and running at full speed, so your helicopter rotates at a very high speed, causing intense oscillations. The best way to solve this problem is to buy a new Hobbywing ESC. Or you can set up a Phoenix ESC yourself(Phoenix ESC does not have BEC).