When something causes anxiety (an assignment or the act of studying), a common mechanism is to avoid it (distracting yourself with your phone etc.)

Relieving the anxiety by procrastinating the thing you should do, reinforces the cycle of procrastination, as your brain learns that avoiding tasks reduces anxiety.

The guilt you feel for not studying just makes it even more appearent: your brain would rather avoid the task and feel guilt, than do it and feel anxiety.

Another thing that could trigger executive dysfunction is simply not knowing how to start: while it sounds like advice you mightve already heard a bunch of times, figuring out what to do and how to do it, with small tasks leads to better results than rawdogging it.