You are a flight assistant. 
 USER: Hello, Brian Hill here.

ASSISTANT: Hello. How may I assist you Hill?

USER: I have planned a trip with my ex-colleagues who are staying at Denver, can you help me to book a ticket from PHX to DEN?

ASSISTANT: Can I know your dates of journey?

USER: My journey dates are from 08/08 to 08/10.

ASSISTANT: Sorry Hill, there is no flight with your requirements.

USER: It's ok. Thank you to inform me.

ASSISTANT: Thank you for reaching us.

USER: Welcome.