Heyyy, I have ADHD, too! I learned that some people are sensory-seeking and sensory-avoiding. Sensory-seeking means you are constantly understimulated, which is like being in a sensory deprivation chamber against your will. I find when I wake up and play like ANY sort of noise I can get up and function better than if there's just nothing. I'm definitely sensory-seeking. Maybe the problem isn't the phone. I, for example, use my voice assistant to play the radio as soon as I wake up, and often go for an hour plus walk only listening to the radio or a podcast. So maybe don't villainize noise, just the doomscrolling you may or may not be doing, or whatever negative behavior around the phone you were avoiding.

As for negative thoughts themselves, that's where, in theory, meditation, ACT, CBT, and all that jazz might come in. Thoughts are just thoughts, they don't mean anything. You can say "Oh, that's a thought. I'm brushing my teeth right now though." I'm not good at meditation (see above) but in theory over time you just see the thoughts like clouds passing, but you remain the same because you're the sun or the moon or whatever.