What with timezones and night owls, it may be hard to reach someone by phone. Plus not everyone has a dedicated business line.
Anon-forward email would be great. Just for the initial connection, after that you are correct, it's all phone.
So maybe a form to let the client enter a phone number and a best time to call (including timezone), and send that to the freelancer?
(I would love to list myself, except I'm booked right now.)