If you have not paid the PSVA in Switzerland a fine of CHF 100.00 will be charged plus the PSVA for the days you have been driving on Swiss roads.
If you simply forgot your phone or print-out of the proof of payment in order to show it, the Swiss police or customs can look up your license plate in the Swiss motorway system
Related articles:
Do I need the Swiss PSVA on ordinary roads?
Are there exemptions for the Swiss PSVA?
How is the Swiss e-vignette checked?