Always return a string value (Zend framework)

/**
 * @readme  I had an issue recently whereby a telephone number was being interpreted as a number
 *      value in the view with the Zend framework, so 01212112121 in the DB was being
 *      displayed as 1212112121 to the user. It may not be the most elegant solution, but this method works.
 * @author  Shaun B
 * @date    2015-09-10
 */

private function getUserPhoneNumber()
{
    $userId         = $this->getUserId();
    $usersModel         = new Application_Model_DbTable_Users();
    $userTelephoneNumber    = $usersModel->getUserPhoneNumber($userId);

    return is_string($userTelephoneNumber) ? $userTelephoneNumber : "0" . $userTelephoneNumber;
}

/**
 * @readme  So, I can now safely pass this to the view with the leading zero, ie:
 */

public function userDetailsAction()
{
    ## Some logic...
    $this->view->userTelephoneNumber = $this->getUserPhoneNumber();
}