Phantom used to be very powerfull spell - that is why many multiplayer games "balanced" / downpowered it (so the phantom image would disapper after first hit - or that the phantom image has "ghost" form - could be missed by 50% chance, but can't dodge fireball) - it was this "balance" that made it less used in battles (Still I remember how I doubled my archangels in HOMM 3 and smashed the strongest enemy stack into pieces of babycry tears)
Here I love that the phantom has all skills/abilities of original (normally it does not have the abilities/ sometime it even does not have special skills - like life stealing etc)
I also like that it has full health (each from phantom unit has normal health of original unit - not less, not 1... )
So my phantom ghosts/phantom vamps can deliver nice fight (also that many spells work on phantom units - like stone skin, magic spring... many games prevent this as they don't take phantom as normal unit - but as spell/ability)
To prove the phantom usefull:
You like undead army? (I do) and wonder how beat Korador with few loses?
1.) Magic Shacle (to remove "dispall" arrows from skell archers - best would be if you fight only one stack of archers
2.) phantom ghosts (if you are not playing for mage - you should first use phantom - let the fly behind your enemy - to attract them - but this would tottally change my strategy)
3.)If you place the ghosts correctly - you should gain even "desorientation" effect and cause AI to get somehow "lost" in da battle
4.) Stoneskin on your Phantom Ghosts (If you placed the phantom gost wrongly - too far - you may experience that you have no phantom ghosts anymore
)
5.) - even as archers and necromancers my shoot behind your phantom ghost --- the loses should not be that great... also archers tend to shoot your army that is nearest -> what is phantom ghost
6.) place magic spring on them (or create new stack if your first phantom is killed) + combine it with "hit and run" tactics - wait with vamps / your real ghosts, hit enemy and as you should start first - Undead Commander skill -> return back
7.) If you can still cast 2 spells even in second round (on Impossible I usually can't) - now you can go for some damage spells (remove archers/necromancers) - let your necromancers to use their necro call on enemy dead (if any) - and again - could be ghosts / cursed ghosts and you may consider enchant them with stone skin again...
as stone skin is cumulative (not like dead armom) with natural defences - your ghosts will have 90% PHY resistance and 50% poison resistance (necromancers have half phy/half magic... still do little real damage) - your stoneskinned ghosts are REAL tank units ...
Why is Phantom so important? - When using BAIT tactics - you have to hand over someone for real damage - non phantom ghosts would not only suffer, also they could not participate on "hit and run" tactics... + enemy shooters have increase random max roll - as you have more stacks, enemy tank units go crazy for your bait, enemy casters usually hate phantom and want to remove it ASAP -> that is why phantom works better as BAIT than normal unit (well, there is this one "Improve AI" MOD - which would probably negate this tactic in huge extend)