Should an undergraduate answer a call for reviewers?
Normally a PhD (in my experience) will conduct their first peer-reviews with their supervisor or another academic. An undergraduate may (rarely) have the technical expertise, but reviewing is also a skill (that doesn't take long to pick up, but requires a bit of guidance). Poor reviews can waste time of committee members or, worse, harm scientific and academic output, and even harm your own reputation. On the other hand, if you contact a member of staff that would be an opportunity to learn how to do it properly and maintain or even advance your reputation at a very early stage in your career.