Phone call options - allow user input (provide own phone number)

The existing "Phone call options" requires me to input my phone number, but I don't want to provide it to the user/booker. Instead this field should allow you to collect the user/booker phone number, so that I can phone them at the meeting time.

I know I can do this via a custom question, but then the "location" section is weird because what would they select then? Calendly provides this exact functionality I describe above.