The telephone screening is the earliest stage in the interview process and the recruiter's role is twofold. She confirms that you're interested in the job and that your work history or experience is consistent with the job requirements. Many recruiters will start the telephone interview with a description of the job and then ask if you're still interested. They follow up with questions about your work experience and qualifications to see if you meet the basic requirements for the job.
Generally speaking, the recruiter's role is to determine whether you're qualified for the position. However, that requires that the recruiter ask certain questions and observe the way you describe your qualifications. For example, recruiters ask behavioral interview questions to gauge whether management candidates really understand the basic principles of how to lead departmental functions and manage employees. A typical behavioral interview question is, "Tell me about a time when you had to delegate an important assignment to an employee whose performance had been declining." From this type of question, the recruiter's role is to see whether you understand how to prioritize departmental responsibilities and how you handle employee issues.
During this final stage in the interview process, recruiters listen to feedback from hiring managers and check references for the top candidates. The recruiter has to draft suitable questions for the candidates' references and determine which candidate is overall best suited for the job based on the hiring manager's preference and information from references.