Ask for reference letter for applying graduate school, professor agreed, but no more follow up
I suspect that he knows of your concern and will come through, though at the last minute. But &quot;repeatedly sending reminders&quot; is also &quot;being a bit of a pest&quot;. Most people will forgive you for that, but not all.
But, he has other things to do and needs to think about what to write on your behalf.
Phoning him will just make it worse, interrupting his schedule.
So long as he knows of the deadline you should be fine. A message a few days before the deadline wouldn't hurt, mentioning your eagerness to know.
But replying to constant reminders just slows down the process, so they are often ignored. It is a mistake to make him less efficient than he could be. Relax for a bit. There is little incentive for him to rush it unless the deadline is immanent.