Finally a Lufthansa thread!
Yay!
Very timely considering how many crew they are hiring this year.
The purpose of a phone interview is getting an overall "feel" of what kind of person you are. It can be five minutes to ten minutes long depending on the conversation. I got this information from an online site dedicated to Lufthansa regional crew recruitment so bear that in mind. There was this post that said the person had to go through a short role play too. In any case being courteous can't go wrong. Just be the better version of yourself! Good luck.