Only PS1 games.
Emulating PS2 requires much more resources, on a PC you need high end hardware to emulate the PS2, and it's not perfect. So far smartphones are not powerful enough to emulate PS2 (but some PS2 games - or their PC versions to be honnest - are already ported to Android, like GTA 3 and GTA vice city)
No PS2 emulator for smarphone exist and there's nothing in developement for the moment.
I think the most powerful console to be emulated on a phone is the Sega Dreamcast (but it's still in early beta developement, maybe only Crazy Taxi is running). Or maybe PPSSPP, the PSP emulator, but only very few games are compatible and you need at least a quadcore to get something about playable.