why can't he have both?
there's more obscure servants that have two noble phantasms...
gates of fire - shield wall, like archer's rho aias, an ultimate defense that can withstand three attacks from any weapon (representing the three days the greeks held against the persian army)
spartan glory - phalanx of the three hundred, summons 300 warriors, each on the level of a rank c saber, to fight for leonidas (rank c, because saber is rank a and she is said to be the most powerful servant in the war in unlimited blade works when she gets a proper master).
so...
class saber
true name: leonidas
sex: male
height/weight: 200 cm 80 kg
alignment: true neutral
strength: a
endurance: a
agility: b
magical energy: d
luck: c
noble phantasm: a
class abilities:
magic resistance: c
(no riding as would be normal for sabers, since sparta's cavalry was not very important)
skills:
battle continuation: a
divinity: d (legend stating spartans are descended from hercules)
instinct: b
charisma: b
bravery: a
noble phantasm:
gates of fire - shield wall:
rank b, type: support, range: -, maximum target: -
a wall of shields that can withstand any attack three times, representing the three days the spartan army withstood the persian army.
spartan glory - phalanx of the three hundred:
rank ex, type: anti-army, range: -, maximum target: -
summons three hundred rank c servants of class saber with rank e independent action to fight for leonidas, representing the legendary three hundred spartan hoplites who fought to the death in the name of their king.
i imagine he'd be fairly weak against servants assassin and caster, considering how iirc he really wasn't exposed to magic the way servants like arturia or cu chulainn would have been.