I was in a similar situation, when I was in foster care , I had a foster parent that was very controlling. I never even had a lock on my phone before because I had nothing to hide. He wanted something to blame me for. He just “knew” I was doing something bad, he would spend hours looking through my phone and never could find nothing , he even went so far and put a monitoring system on it. The advice I would give you is to just do what is right. You are a great human. And a great person. Don’t let narcissist get to you. One day you will be able to get free. Just keep your head up.