I'd like a setter for number, and this method can simply set the number and hit call. Then you can set in the test without hitting call.

    @property
    def phone_number(self):
        return return self.marionette.find_element(*self._phone_number_view_locator).get_attribute('value')

    @phone_number.setter
    def phone_number(self, value):
        # code to set phone number

    def call_number(self, value):
        self.phone_number = value
        self.tap_call()