One problem when I work is that I work with extreme focus for an hour or to until I burn out, at which point I stare at my phone for a long time. The pomodoro method reminds me that things are a marathon, not a sprint.
Before you go on a break, decide what task you’re going to do next and open the resources you need for that task. Before I did that, I’d just keep lazing about in my break because the cognitive load of “starting a new task” stopped me from wanting to finish my break. Now, I finish my break and hop right into what I need to do.
Adding a delay to the opening of my social media apps, preventing me from just impulsively opening them. (On Android I use the “IChooseTo” app)
Plan out tasks you want to get done by the end of the day, end of the week, and end of the month. Keeps yourself grounded in a PhD.