public function getCellPhoneNumber()
    {
        $mobil     = null;
        $mobilsRaw = $this->getFlexiData($this->getApiURL(),
            ['detail' => 'custom:id,mobil,kontakty(primarni,mobil)', 'relations' => 'kontakty']);
        if (is_array($mobilsRaw)) {
            $mobils = $mobilsRaw[0];
            if (array_key_exists('mobil', $mobils) && strlen(trim($mobils['mobil']))) {
                $mobil = $mobils['mobil'];
            }
            if (array_key_exists('kontakty', $mobils) && !empty($mobils['kontakty'])) {
                foreach ($mobils['kontakty'] as $kontakt) {
                    if (($kontakt['primarni'] == 'true') && strlen(trim($kontakt['mobil']))) {
                        $mobil = $kontakt['mobil'];
                        break;
                    }
                }
            }
        }
        return $mobil;
    }