Hello Yaiyuewai53
Firstly, welcome to the SBB Community.
It is recommended to print international tickets for the event when your device does not have sufficient battery while travelling and you cannot recharge it or in case the ticket code cannot be scanned by the train staff.
If you can assure that you will have sufficient battery, you are welcome to use the PDF ticket saved to your device. Make sure you have your physical passport or government ID always with you when travelling with e-tickets.
Kind regards,
Roland