I don’t know which train I lost it on, as I had several transfers. First, I took the R62 from Lauterbrunnen to Interlaken OST at 6:01 PM, then the IC61 from Interlaken to Bern at 6:29 PM, and finally the IC1 from Bern to Zurich Main Station at 7:31 PM, before finally taking the S4.
I lost a black iPhone 12 with a white piece of paper taped to the back.