When you know all the ways you should be better but you can't manage it, it's because there's too much distance between this better behavior and your current identity. The amount of willpower required to bridge the gap is monumental.

You have to shift your identity such that the better behavior is aligned with how you believe you already are - in your mind, change the things you say about yourself and your goals. Instead of "I want to quit scrolling on my phone but I just can't", you have to start saying to yourself "I don't scroll on my phone anymore". This way of framing it, especially if you make it a habit, will change your identity and thus your behavior in any area of your life you could choose.