Many employers conduct telephone interviews to screen candidates for basic qualifications. It is also an alternative when it is not practical to invite an out-of-area candidate to the office.
Telephone interviews can be challenging because it is more difficult to gain rapport with the interviewer because you cannot see the interviewer's non-verbal reactions and cues. Conversely, the interviewer cannot see your enthusiastic expressions or professional appearance. This places all the weight on your phone manners, clarity of speech, voice tone and the content of your answers.