Can Saving Finale be used to save another creature from Phantasmal Killer?

Question

The bard spell Saving Finale lets the bard end his performance to let one of the performance's targets reroll a failed save:

DESCRIPTION

You must have a bardic performance in effect to cast this spell. With a flourish, you can immediately end your bardic performance when a creature within range affected by your bardic performance fails a Saving Throw, allowing the subject to immediately reroll the failed Saving Throw.

The question is, how does the bard know that the creature that he wants to help has failed a save? Phantasmal Killer reads:

DESCRIPTION

You create a phantasmal image of the most fearsome creature imaginable to the subject simply by forming the fears of the subject’s subconscious mind into something that its conscious mind can visualize: this most horrible beast. Only the spell’s subject can see the phantasmal killer. You see only a vague shape. The target first gets a Will save to recognize the image as unreal. If that save fails, the phantasm touches the subject, and the subject must succeed on a Fortitude save or die from fear. Even if the Fortitude save is successful, the subject takes 3d6 points of damage.

If the subject of a phantasmal killer attack succeeds in disbelieving and possesses telepathy or is wearing a helm of telepathy, the beast can be turned upon you. You must then disbelieve it or become subject to its deadly fear attack.

Since only the subject can see the phantasmal killer, if the bard fails his Spellcraft roll to identify what the enemy is casting, does he miss the chance to save his ally?

Answer 1

Saving Finale is weird

Strange title, right? But it's true... Saving Finale works "because magic". Moreso than other magic, anyway. Specifically, it allows Bards to react to something that they are not aware of and, by the rules, do not know about. Specifically, Bards do not have any way (outside of meta) to know when a creature has failed a saving throw (except against their own spellcasting).

So, when you cast Saving Finale, there doesn't need to be any obvious failure of Saving because the spell doesn't say so, nor give guidance on how to know. At a GM's discretion, you may not be able to cast it in response to spellcasting you're entirely unaware of (such as Scrying) but there are no rules regarding it, so its up to table variance.

Additionally, not being able to see the Phantasmal Killer is not the same as not knowing that a spell has been cast on a creature, nor would it affect your (meta) knowledge of how well their Saving Throw(s) went.