Like Glenys, I haven’t had a phone interview from Admiral specifically, but I suppose the same rules of phone interviews will still apply.
Make sure you’ve done some previous research on their company and are ready to answer any questions they throw at you.
A very good tip is to have all the paperwork you need in front of you. This is one of the reasons why people think phone interviews are so much easier than face-to-face interviews. You can regularly refer to your CV and other print-outs that you have without the interviewer knowing.
Good luck with your interview!