Clearing: phone interview or ??

When you apply through clearing do they always give a phone interview
how wil i know if it is an interview or a friendly question like

i might be saying hi how r u blablabla
then they might politely ask why this course
-should i actuallyanswer that question as i would in an interview [like a paragraph]
or would i answer that question casually like about 3 lines.

Note: Imagine if i answer it casually i know it is just casual but i dont want them to think that that was it or something

help thanks

You will firstly be screened by the front line staff, who will direct your call to the appropriate admissions staff, so you will know when you are speaking to someone who is interviewing you. Follow their cues from then on.