This has been my experience:
Delete apps that shorten your attention most, bit cliche but it works. I wouldn't say delete all because that is more likely to lead to failure. Just got to recognise that if you are training yourself to watch sub 1 minute videos then don't expect yourself to maintain attention for much more than that, so choose the app that is the 'worst' and just ******* get rid of it. If u like u can slowly keep deleting apps every 6 months maybe.
Try out apps like flora or forest. They basically create a timer in which you cannot use your phone. I would favour this over simply powering your phone off both because it is more secure, but also because we are still lowk monkeys and seeing a little reward (the tree u get after a timer) is a positive reinforcement.
As you said meditation is a good help. I would recommend the app "medito", you should follow their introductory course it is very good. It starts of quite light with 3 minutes, and builds up to the concepts that genuinely change how you think about focus.
You can try creating a 'environment' in which you study, keeping this separate from your other spaces, depending on how niche u want to go. Supposedly it compartmentalises it so that when you are in that 'environment' your brain is in 'focus mode'.
Quality revision not quantity. Maximise the worth an hour can give you and you wont be stuck revising in your room for 6 hours plus a day.
Do work as soon as possible each day, then you can actually enjoy other things. (ie when you wake up or as soon as you get home)
Finally, take it slow and build consistency, start with maybe 1 hour a day (but never miss a day, regardless of obligations, just do it as soon as possible), then escalate it up. For GCSEs if you revise 2 hours a day every day for year 11 you should get minimum straight 8s, assuming you make you work 100% productive.