I haven’t got any info on the Atkin telephone interview specifically, although there is information about the rest of the assessment process on the wikis. See - [[Atkins]]
I recommend reading this article on [[telephone interview]]s and this article on [[competency based questions]] as your telephone interview will almost certainly feature them.
The interview will almost certainly be relatively short (20 - 30 mins) and you should be able to explain why you want to work for Atkins, why you want to work in this industry, and you should also be able to talk about [[commercial awareness]] type (business) issues about your industry.
Also, familiarise yourself with your CV as this will probably also be discussed.
Good luck! Let us know how it goes!