If you're referencing this line:
In addition, after you summon Phoenix for the first time, there's a small chance that when your party is KO'ed during battle, Phoenix will revive you.
then no need to fear. If you've never used a Phoenix Pinion, the Phoenix GF will not show up to help you, ever. So when I say "a small chance," I mean there's a chance she'll show up, rather than there being absolutely no chance. By using just one, Phoenix may show up when your party is KO'ed, otherwise, she never will.