Remember the golden rules:
Modern emulators support specific formats that decompress data on-the-fly, meaning you don't need to manually unzip them before playing. AetherSX2 for Android - Download the APK from Uptodown
To get you started, here are the top-tier PS2 games that are naturally small or compress incredibly well, perfect for any Android SD card:
Highly compressed PS2 ROMs are game files that have been re-encoded to reduce their file size significantly without sacrificing the ability to play them on an emulator.