If you download the manual from the Phillips site, it shows that model to have a DVI input. If it's a DVI input that's compatible with the G5's DVI output, then, in theory, it should work. Real-life is a different story, though... it may work with astonishing results, it may work with disappointing results, or it may not work at all.
Best bet is to call Phillips and see if they express compatibility with your G5 machine.
This is true -- that TV you just listed may probably work with your PowerMac G5, but it will look like crap. The maximum resolution when used as a monitor is 800x600... that would be ridiculous and unusable.
If you want a good flatscreen TV/monitor combo, get yourself a good quality flat-screen LCD computer monitor -- not a TV monitor. Then, invest in ElGato's EyeTV stuff and you can get TV on the monitor -- rather than the other way around.