Hi ChrisG85! I recently applied for a Phd Studentship and was successful so maybe my tips would be helpful to you! In my cover letter I wrote mainly about why I was applying for this particular phd studentship, what skills I had to enable me to see this research to completion, my research interests and interest in this particular research area and why I chose this particular university to apply to. I have been told that the aim of a cover letter is to sell yourself without being over confident and cocky! Also google cover letters for phd application - I got some useful tips this way! Hope this was of use to you. Best of luck with your applications!