Trying this

Stripe.customers.update(customer_id, {
        "metadata.city":            form['address.city'],
        "metadata.state":           form['address.state'],
        "metadata.address_line1":   form['address.address_line1'],
        "metadata.address_line2":   form['address.address_line2'],
        "metadata.postal_code":     form['address.postal_code'],
        "metadata.phone":           form.phone
    }, function (error, customer) {
        if (error) {
            //console.dir(error);
            stripeCustomerUpdate.return(error);
        } else {
            stripeCustomerUpdate.return(customer);
        }
    }
);

Getting this error in the dashboard
error:
type: "invalid_request_error"
message: "Received unknown parameter: metadata.phone"
param: "metadata.phone"