Generally, I find the phone/video initial interviews are done in response to a history of inviting poor applicants to interview in person. More specifically, departments usually have a limited amount of time and resources to interview applicants in person (e.g., you are competing against other programs for quality faculty, you are allocated only so much $ to pay for visits, and everyone has to move their schedules around to fit in an interviewee[probably the most difficult]). Usually, 3 or 4 people are interviewed in person. If, in the past, a program has had some applicants show up that are quickly identified as a poor fit for the job (e.g., difficult personality, CV poorly represented the ability of the applicant, applicant not really all that interested in the position), the program has now wasted 25%-33% of your resources.
Those programs want to maximize their resources and have in person interviews with applicants that fit the culture of the program, are actually good at their job, and actually want to be there. I think that is the purpose of the phone/video pre-interview.