Emulators don’t actually emulate the BIOS — they load a real dump of it to handle:
The SCPH5500.bin is the BIOS file specific to the SCPH-5500 console. The BIOS (Basic Input/Output System) is a crucial component of the console, responsible for initializing the hardware and providing a interface for the operating system. Playstation Scph-5500 -v3.0 Japan- Bios Scph5500.bin