You don't lose the game for having 0 or less life. As long as you have 0 or less life, all damage is dealt to you as though its source had infect. (Damage is dealt to you in the form of poison counters.)
原文Phyrexian Unlife won't affect damage that reduces your life total from a positive number to 0 or less. For example, if you're at 3 life and are dealt 5 damage, you'll end up at -2 life. The next time you're dealt damage, it will be dealt as though its source had infect.