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.
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.