Surprisingly, despite the existence of
Acmlm's run, there is not already a thread about this game.
Based on
this irreverent review and the lack of a video showing off the sequence break in which you trade your boots for an Escapipe, use that in the dungeon at the beginning instead of talking to the person on the other side of the grate, and find out you cannot continue the game, I made a non-tool-assisted demonstration movie showing how to do it and what parts of the game you can still explore after you're done.
GMV:
http://dehacked.2y.net/microstorage.php/info/1996992728/UnwinnablePSIII.gmv
MKV:
http://www.mediafire.com/file/zcgllmi2yzk/UnwinnablePSIII.mkv
DailyMotion:
http://www.dailymotion.com/video/xbqbsm_phantasy-star-iii-gamebreaking-expl_videogames
The video is just over 13 minutes long, but if the basic route were TASed (like going through the entire basement, collecting all of the items, taking both exits, talking to the king at least once, meeting up with Maia again, and trying to exit town), it might be able to be short enough for YouTube.