Then you may need to either put blockers in your phone, that prevent you from entering certain apps and websites during certain periods of time. Maybe to lock away and leave your phone somewhere else, like in a drawer or something.
I honestly don't understand much what kind of advice are you specifically looking for since your replies and post itself are extremely short.
Well, if the problem is sitting alone and doing nothing then they just have to occupy their time doing something else, no matter how grand or non-important it is, sometimes you have to do something even if its insignificant but at least to avoid routine or simply cut down another action.
My go-to break from social media is simply doing errands, housechores, play video-games or take care of my cats, personally I can sit down and do nothing like staring at a wall or just drink some coffee while looking out my window.
But I get that stuff seems to be too mundane for others, therefore they just feel bad doing nothing. And I think that should be addressed in therapy, with professionals since its usually attached to feeling of guilt and overachievement. I go through that too myself but learned to just not punish myself if I do nothing, especially since I have days of executive dysfunction, I even put reminders at time to drink water or put everything I need near me so even walking a few steps is not a tremendous task. No matter how dumb or childlike, if it helps you cope there is nothing wrong with that.
But again, I don't think any advice is going to be even 50% helpful, since we don't know you and this post itself seems to be way too vague. Kinda hard to know from which angle to tackle it.