[notyourwork]

Interviewing is an expensive process so you try to introduce multiple steps which filter a large candidate pool down to a hire. If every candidate with a resume that indicated they were qualified was brought in the process expense would increase drastically.

Furthermore, phone screen allows ability to get perspective on soft skills. At least in my field, technical people need to communicate and therefore a phone screen allows ability to review this attribute of candidate which isn't conveyed on a resume.