How to use the gaiatest.apps.phone.regions.call_screen.CallScreen function in gaiatest

def tap_phone_number(self):
        call = self.marionette.find_element(*self._call_phone_number_button_locator)
        Wait(self.marionette).until(expected.element_enabled(call))
        call.tap()
        from gaiatest.apps.phone.regions.call_screen import CallScreen
        return CallScreen(self.marionette)

def tap_call_button(self, switch_to_call_screen=True):
        element = Wait(self.marionette).until(
            expected.element_present(*self._call_bar_locator))
        Wait(self.marionette).until(expected.element_enabled(element))
        element.tap()
        if switch_to_call_screen:
            return CallScreen(self.marionette)

def a11y_click_call_button(self, switch_to_call_screen=True):
        self.accessibility.click(self.marionette.find_element(*self._call_bar_locator))
        if switch_to_call_screen:
            return CallScreen(self.marionette)

def call_screen(self):
        from gaiatest.apps.phone.regions.call_screen import CallScreen
        return CallScreen(self.marionette)

def tap_search_popup(self):
        self.marionette.find_element(*self._search_popup_locator).tap()
        return CallScreen(self.marionette)