Monkwarrior is faster than me, anyway I'll add..
How does one remove Phalanx formation and make all Phalanx units fight like spearmen?
Open EDU, find unit's entry, and remove "phalanx'' atribute. Also remove short_pike or long_pike attr.

Eg. Bronze shields entry
Spoiler Alert, click show to read: 

type east hoplite brazen shield
dictionary bronze_shield ; Bronze Shields
category infantry
class spearmen
voice_type Heavy_1
soldier greek_bronxe_shield, 60, 0, 1
officer east_heavy_standard
attributes sea_faring, hide_forest, can_sap, hardy
formation 1, 1, 2, 2, 8, square, phalanx
stat_health 1, 0
stat_pri 10, 4, no, 0, 0, melee, blade, piercing, spear, 25 ,1
stat_pri_attr spear, long_pike, spear_bonus_8
stat_sec 5, 3, no, 0, 0, melee, simple, piercing, sword, 25 ,1
stat_sec_attr no
stat_pri_armour 6, 6, 2, leather
stat_sec_armour 0, 0, flesh
stat_heat 0
stat_ground 2, 1, 0, -1
stat_mental 8, disciplined, highly_trained
stat_charge_dist 30
stat_fire_delay 0
stat_food 60, 300
stat_cost 2, 690, 360, 70, 110, 690
ownership pontus


should be
Spoiler Alert, click show to read: 

type east hoplite brazen shield
dictionary bronze_shield ; Bronze Shields
category infantry
class spearmen
voice_type Heavy_1
soldier greek_bronxe_shield, 60, 0, 1
officer east_heavy_standard
attributes sea_faring, hide_forest, can_sap, hardy
formation 1, 1, 2, 2, 8, square
stat_health 1, 0
stat_pri 10, 4, no, 0, 0, melee, blade, piercing, spear, 25 ,1
stat_pri_attr spear, spear_bonus_8
stat_sec 5, 3, no, 0, 0, melee, simple, piercing, sword, 25 ,1
stat_sec_attr no
stat_pri_armour 6, 6, 2, leather
stat_sec_armour 0, 0, flesh
stat_heat 0
stat_ground 2, 1, 0, -1
stat_mental 8, disciplined, highly_trained
stat_charge_dist 30
stat_fire_delay 0
stat_food 60, 300
stat_cost 2, 690, 360, 70, 110, 690
ownership pontus


Also how would I go about turning basic warband into spearmen,
Eerr, you want phalanx? Than instead of this
Spoiler Alert, click show to read: 

type barb infantry gaul
dictionary barb_infantry_gaul ; Warband
category infantry
class light
voice_type Light_1
soldier barb_infantry_longshield, 60, 0, 1.2
officer barb_standard
attributes sea_faring, hide_improved_forest, warcry
formation 1.2, 1.2, 2.4, 2.4, 5, square
stat_health 1, 0
stat_pri 7, 4, no, 0, 0, melee, simple, piercing, spear, 25 ,0.73
stat_pri_attr light_spear, spear_bonus_4
stat_sec 0, 0, no, 0, 0, no, no, no, none, 25 ,1
stat_sec_attr no
stat_pri_armour 3, 2, 5, leather
stat_sec_armour 0, 0, flesh
stat_heat 3
stat_ground 2, -2, 3, 2
stat_mental 4, impetuous, untrained
stat_charge_dist 40
stat_fire_delay 0
stat_food 60, 300
stat_cost 1, 420, 200, 50, 70, 420
ownership gauls

make this
Spoiler Alert, click show to read: 

type barb infantry gaul
dictionary barb_infantry_gaul ; Warband
category infantry
class light
voice_type Light_1
soldier barb_infantry_longshield, 60, 0, 1.2
officer barb_standard
attributes sea_faring, hide_improved_forest, warcry
formation 1.2, 1.2, 2.4, 2.4, 5, square, phalanx
stat_health 1, 0
stat_pri 7, 4, no, 0, 0, melee, simple, piercing, spear, 25 ,0.73
stat_pri_attr light_spear, short_pike, spear_bonus_4
stat_sec 0, 0, no, 0, 0, no, no, no, none, 25 ,1
stat_sec_attr no
stat_pri_armour 3, 2, 5, leather
stat_sec_armour 0, 0, flesh
stat_heat 3
stat_ground 2, -2, 3, 2
stat_mental 4, impetuous, untrained
stat_charge_dist 40
stat_fire_delay 0
stat_food 60, 300
stat_cost 1, 420, 200, 50, 70, 420
ownership gauls

They will fight as small phalanx with charges, but I don't think it will increase their perfomance, you still need swordsmen.
Or you can remove "short_pike" and they will be a phalanx (like vanilla german spearmen)