Yes it is. You can use those media to communicate if it is a mutual agreement, but you certainly aren't required to use them. Upwork has their own propierity video and voice messaging system that you can use:
Just tell them you'd be more comfortable using Upwork's system.
Yussuf A wrote:
Is it appropriate to say " I don'thave Skype " to client asking for Skype call and provide WhatsApp contact instead
You don't have skype? Whyever not?
I'd never use WhatsApp to communicate with clients, as it gives complete strangers access to my phone number.