Phyletichoi Illyroi (Illyrian tribesmen) are not simple spear levies — they are not as heavily armoured as Hoplitai Haploi, but have a propensity for countering enemy heavy infantry and are also faster on foot. Be their enemie Greek hoplites or Celtic-style neitos, they all face the same prospect of being killed or severely scratched by these hardened tribesmen.
Thus Phyletichoi Illyroi are idea infantry-busters, and are meant to be used as aggressively as possible. In the hands of a skilled Epirote player, they can be used to charge an enemy's heavy infantry or cavalry, giving a window of opportunity for a cavalry strike on softer targets that those units were otherwise fighting. Still, while they are very fast cavalry-killers, they are utterly worthless if attacked at ranged, especially with ranged cavalry.
Historically, the Illyrians were a people that inhabited the northern part of modern day Albania and were bordered in the south by the Greeks of Eprius and Aetolia, and in the east by Macedon and Thessaly. Thus, they had to adapt their warfare to fight these enemies, a task they became frighteningly good at to the extent that they could form a kingdom of their own at the expense of their Greek neighbours. The Macedonians, once reasserting their dominance, wisely recruited these hardened warrior tribes for their own ends. Fairly large contingents of Alexander the Great's light infantry in the Persian conquest were of Illyrian extraction.
Following his death, they won their independence once more after Alexander’s death, but were soon broken by the Celtic invasions that followed his death and were never again to become a major power. Subsequently, Illyria became the first Roman province outside of the western Mediterranean. The Illyrians adapted quickly to Roman culture and became the first extremely loyal non-Italic subjects of the growing Empire.