Send custom fields to MailChimp

Hello,

I’m wondering: how’s the plugin pushing the checkout fields to MailChimp? I mean, I guess that the First Name, Last Name and Email are passed via the usual FNAME, LNAME and EMAIL.

But what about other fields?

For example, in my checkout I’m also asking the customers to leave their phone (optionally) and country. Is there a way to push this fields to MailChimp too?

Thanks.