If the router phone book on your Fritzbox or other CAT-iq router does not open even though you press and hold the phone book button, there could be several reasons for this.
Check the phone book function: Ensure that your Gigaset telephone is configured correctly to access the router phone book. Sometimes this function must be activated manually in the settings of your router.
Correct DECT settings: Ensure that the DECT settings on your Fritzbox are correct and allow Gigaset phones to access the router phone book.
Router configuration: Special access rights for phone books can be set in the Fritzbox user interface. Ensure that your Gigaset telephone has the necessary access rights granted in the router settings.