Short answer is yes, in my opinion. You need to demonstrate things such as ability to communicate, subject knowledge, interpersonal skills, enthusiasm... These things can't always be determined from CVs/cover letters - that's why there is an interview. The basic requirement is your qualifications, decent proposal etc - everyone who gets to the interview stage will have this. You have show why they should employ you over the other candidates.
Think how you could have improved your performance from the last interview, and use this as an opportunity to develop further. If you get this PhD, great, if not, consider it more experience and use it towards your next interview.
Read up online about interview technique, think of questions you may be asked and practice answering them. Show you want this position and make them like you and it's yours. Good luck :)