That lack comes about largely due to the fact there are few passages in the sources describing the phalanx actually at work and, more so, just how it worked. One has to deduce from implications in the material just what is going on and how.
Diodorus – amongst others – is replete with phalanxes (Macedonian) “falling heavily upon” the opposition and “cutting them to pieces” in what is usually described as “hand to hand fighting” where the phalanx is “not to be checked in their charge”. Such laconic descriptive language, in a few words, summarises much action and bloodletting.
Arrian too leaves us largely guessing and his occasional glimpses simply tease. Gaugamela is as close as he comes to describing the phalanx in action:
Alexander wheeled round towards the gap, and forming a wedge as it were of the Companion cavalry and of the part of the phalanx which was posted here, he led them with a quick charge and loud battle-cry straight towards Darius himself. For a short time there ensued a hand-to-hand fight; but when the Macedonian cavalry, commanded by Alexander himself, pressed on vigorously, thrusting themselves against the Persians and striking their faces with their spears, and when the Macedonian phalanx in dense array and bristling with long pikes had also made an attack upon them, all things together appeared full of terror to Darius…
“That part of the phalanx” is clearly the hypaspists and, as we later find out, Koinos’ aesthetairoi. Later he tells us that the two taxeis of the left of the line are unable to follow as they are loath to leave the left wing in dire straits. More likely they were rooted to the spot with the Persian assault pinned upon their sarissae. The Hydaspes account too shows the phalanx, apparently, stepping back and assuming
synaspismos for the final liquidation of the rajah’s trapped army.
Polybios (19.21.1-3 via Kallisthenes) tells us of the evolutions of the phalanx as it deployed upon the widening plain of Issos. Here it forms from column into a ‘double phalanx’ (32 deep) then into 16 deep and finally, likely to cover the field, eight deep.
In the later Hellenistic period we have Plutarch’s description (via Scipio Nasica) where Perseus’ phalanx “charges” the Roman maniples and plants their sarissae into the Romans through both shield and breastplate (18.19.1; 20.3-4). Polybios also relates the performance of Philip V’s phalanx at Cynoscephalae. Here Philip gathers that part of his phalanx that has formed up and orders it to double its depth and to “close up to the right” (18.24.8). This would be what Polybios means in his description of Issos where, had the phalanx eight deep formed synaspismos, it will have taken up only half the width of its earlier formation (close order). Polybios also describes the forming of the "double phalanx" by Gonatas at Sellasia (2.69.8-9) though, typically, he does not describe the detail of the evolutions.
After that we are left with the “Tactical Manuals”. These are written well after the event and envisage a geometrically perfect and faultlessly drilled phalanx operating in the perfect world. This is not to discount same, but, to take them at face value is to buy that marvellous three room tent and expect it to set up on the undulating surface of the average camp ground exactly as it did on the perfectly level floor of the showroom.
I will send you Rahe when I get home tonight.