[split] Phalanx warfare: use of the spear

[Crispianus]

2cm thickness? that would make it quite heavy i suppose.. any tests been made against such armor?

Some observations...

Uncompressed oak tanned Bovine leather 8mm thick is approx 2Lbs(900grms) a square foot(300x300mm) by my estimate you would use about 6 square foot (12 Lbs)more or less, 2 back, 1.5 front, 1 sides, 1 shoulders combined with back.
The thickness can be tailored by adjusting the thickness by extra layers, thinning or by using thinner material on less exposed or reinforced areas, the body could be made from several pieces joined together or one piece adjusted for thickness where appropriate, the front or any area could be reinforced with raw hide ...
Felt could be used as a backing...
The Pteruges: leather or a strip woven material such as tablet weave(see image), I appreciate that this image is not Greek:
    Image credit RomanHideout.com

Weapon penetration(speculative: although I did try a steel spike with a long thin point as hard as I could strike overhand on two layers against a wooden block, but it has no weight! it pentrated one layer about 5-6mm)
I need a razor edge to cut this material and some force to open the cut, a sword or spear point I think would be somewhat blunter, a sword thrust IMHO wouldn't stand much chance, a spear would likely penetrate one layer and  would likely be stopped by a second layer, though this would depend entirely on the weight and power of the blow and the type of spearhead.

so I would say on this unhardened leather, one thickness would provide minimal protection against a spear thrust more if a double layer is used or if the leather is hardened, doubled, or has a shock absorbant backing of any kind... even if the armour was pentrated the attacker may well find themselves with the spear stuck in their opponent as it would tend to stick in the leather.. and that fraction of a second struggling to free it could easily result in injury by a second opponent targeting the armpit...

Apart from any protective qualities it might give, Armour such as this may act more as deterrant forcing the opponent to a pick a more exposed area as and when chance allowed... for me this would be the thigh, neck or shoulder region not covered by protection, a meaningfull strike to the unprotected area of the shoulder would effectively disable/disarm the opponent...

The downside:
Such thick veg tanned leather could take years to tan if such a tanning method was available at this time, the current archaeological evidence would point towards this not being the case though it could be possible that the Greeks had access to it, in any case thick leather suitable for shoe soles was available.
The other possiblity is that such armour is made from Rawhide or partially tanned or cured with a rawhide core, or wholly oil tanned leather such as Buff....

Note: Vegetable tanned leather is well established  from surviving leatherwork from the late first century BC at least.

Edit: Theophrastus (371-287bc) in his book "Enquiry into plants" mentions Vegetable Tanning from a variety of sources including Oak Galls, Pine Bark and Acacia Pods and Sumach(white leather) and Alder(possibly red) for dying.
Original credit: C. van Driel-Murray " Leatherwork and Skin Products" in "Ancient Egyptian Materials and Technology".
https://archive.org/details/enquiryintoplant01theouoft