An emulator is software that mimics the hardware of the PS2 console. You then feed the emulator a copy of the game disc (the ROM/ISO), and the emulator runs the game on your phone hardware.
Emulators (like AetherSX2 for PS2 or Dolphin for Wii) are legal software. However, downloading games you don’t own is not. If you own the original disc and dump the BIOS/ROM yourself, emulation is generally considered legal in some countries (like the US under fair use for backups), but sharing or downloading ROMs remains illegal. descargar dragon ball z budokai tenkaichi 3 para android rom