Ok, let us make you understand that why it is important to be focused on Phone Interview as well.
Not all companies will go with Telephonic interview, but there are certain companies will do phone interview before meeting you in person. So, when you are in search of job it is also important to be prepared for telephone interview. Usually this is a process to discuss the job details and also to know if the candidate is interested with the job profile.
Sometimes you may receive the interview schedule through email, message or by phone call. Also, you cannot predict when the recruiter will call surprisingly. Do not have a creepy (wired songs or dialogues) kind of ring tone.