I'll take a crack at making some ideas.
Corsair's Roll: Significantly increases the exp bonus on a chain.
Ninja Roll: Occasionally allows a person to hit the monster upon when the monster attacks and misses. Like WAR's Retaliation, but applied to monster's missed hits.
Hunter's Roll: Addition Accuracy bonus given if a hit misses (Like WHM's auspice + misery.)
Chaos Roll: Occasional 2x Damage on physical attacks.
Magus's Roll: Occasionally reduces damage from a magical attack and that damage prevented is converted into MP.
Healer's Roll: Restores 33% MP instantly and applies normal Hmp bonus when resting.
Puppet Roll: few ideas
1) Occasionally damage dealt to pet is reduced to 0.
2) Pet get Regen, Refresh, Regain effect.
3) Chance for pet to be immune to all enfeebling effects.
Choral Roll: An increase to all base stats (str,dex, etc..) This is probably the least used phantom roll out there. The increase would have to be quite significant for this roll to be used.
Monk's Roll: Occasionally recudes the TP that would be received by the monster from a melee attack to 0.
Beast Roll: Pet will occasionally do 2x damage on a physical hit. Increase to pet's STR/DEX/AGI/VIT stats.
Samurai Roll: few ideas
1) Addition effect damage based on the amount of TP.
2) Occasionally gives an extra 10TP on an attack.
Evoker's Roll: Possible chance to completely restore all MP to party members in range.
Rogue's Roll: Physical weaponskills that normally can not crit, have a chance for the hit(s) to crit.
Warlock's Roll: Occasionally gives bonus magically accuracy to a spell being casted.
Fighter's Roll: The damaged from the 2nd hit when Double Attack procs is 2x.
Drachen Roll: Occasionally 2x damage from magical attacks. I'm unsure if Drachen Rolls effects Healing Breath, if so, increase the amount restored by healing Breath also. Additional increase to the pet's INT/MND/CHR stats.
Gallant's Roll: Chance for complete damage reduced to 0 and for all of that potential damage to be dealt back onto the enemy.
Wizard's Roll: Full benefits of day/weather of the magic spell of the same element.
Dancer's Roll: Instantly restores 33% HP and applies normal regen effect.
Scholar's Roll: Spells of the same element as Weather/Day have a higher chance to cost only 1mp when it's casted.
Bolter's Roll: grants a costume effect, that makes players immune to monster aggroing. I was thinking the effect given at some of the in-game festivals.
(fun idea: give tracer effect of character when running, like blur motion)
Caster's Roll: Occasionally grants Quicken (instant cast) to a spell.
Courser's Roll: Range attacks that snapshot consume no ammo and deals 2x damage.
Blitzer's Roll: Chance for a hit to have 0 delay, allowing for the next swing session to immediately start.
Tactician's Roll: Instantly gives 100TP and applies regain bonus.
Allies' Roll: Allows Skillchain effect "Light" and "Darkness" to continue each other's chain. Different from a relic/emp weaponskill, where several people can go Fragmentation -> Light -> Relic/emp's Light. This will also allow Light -> Darkness.
Chocobo Roll: Upon a roll of 11, grants party members a chocobo costume (completely made up roll), actually... bolter's roll