Downloading BIOS files from the internet is a legal "gray area" because they are copyrighted Sony software. The official way to obtain a BIOS is to "dump" it from your own physical PS2 console.
The SCPH10000.BIN file is a specific version of the PlayStation BIOS, which was released for the PS1 console. The "SCPH" prefix stands for "Sony Computer Entertainment, PlayStation Hardware," and the number "10000" refers to the specific version of the BIOS. scph10000.bin download for android
Using your file manager: