Bottom line (and people keep forgetting this) is that Tesla has publicly stated that Autopilot software is not complete nor completely tested and has not been released. Drivers (including me and you) who use Autopilot have to select a button that enables it in the menu and it explicitly states that this is Beta software...meaning you are testing software that has not been finalized yet. As such, the fact that it may phantom brake, steer oddly, or do other things, is totally in bounds (from a legal point of view) and YOU not Tesla are choosing to operate test software on the road environment recognizing (and accepting) liability for things the car may do because it is under your control. There are many on this list who have complained that Tesla is keeping Autopilot in Beta purely to protect themselves legally. While that may be true, I think the number of problems that Autopilot still has would point to the fact the software really is still in Beta and be more concerned if Tesla called the current software "Final".
As such, your comments that the phantom braking on the highway are a safety issue are correct, but they are a safety issue on YOU not Tesla, because you are choosing to operate test software in that environment.
As others have said, the other issues you have with your car may well support a lemon law claim (none of us can judge because you haven't shared them) but the phantom braking/autopilot issues you are seeing are not grounds for a lemon law claim because Tesla has not yet delivered a product to be defective...they are merely giving you the option of an advance preview/test of the current test software...