New to the XIAO nRF52840 here and chasing the low power shutdown options.
The schematic Seeed Studio XIAO nRF52840 v1.1 shows the USB Phy block as USB1. In the same way as the block for the flash chip U2.
Ahhh… It has just occured to me that USB1 may just be the symbol for the USB-C connector and that you are correct that the nRF52840 main silicon does all the USB signal processing.
Onwards 