In case your mobile phone is not functional, you simply show the red SwissPass card.
You do not have your SwissPass card with you? As stated in the GTC’s, it is mandatory to have the red SwissPass card or an official ID card with you at all times when using the SwissPass Mobile (e.g. through the SBB Mobile app); the SwissPass Mobile is only valid if you can proof your ID or can show your red SwissPass card. The ticket inspectors can always ask for it.
See: Swiss Pass Mobile
Thanks to the SwissPass card your GA travel card can be checked through the card. If you only have an official ID, you will have to pay a CHF 5 fee for the replacement GA card.