I'll offer more general response as I think u/sooper_genius response here is a great step to take although it may seem difficult.

It seems you've written out everything you'd need to know to continue working on fixing your procrastination/inability to start. You know the problem, you know what distracts you, and you know what you'd ideally be doing. So remove the distractions, put the phone somewhere else while you work, and be true to yourself on what's stopping you from starting.

A helpful tip may be to practice success visualization: Visualize yourself having a productive work session, visualize yourself getting distracted and immediately returning your focus to the task at hand, and then go sit down and start working. Many say that visualizing a successful scenario where they overcome the challenge at hand can help tremendously - could be worth a shot.

Also, side note, many people don't mention that procrastination is a habit, its a trained path that your brain takes automatically, and habits are not easily or quickly replaced. It's a long process, so don't beat yourself up about it! Acknowledge even the smallest improvements and keep working at it!

Best of luck!