OK, let’s start venturing some tentative military demographics and see how well they hold up. I’ll also share some of the bigger demographic picture so y’all can critique my worldbuilding, but I need to immediately add the caveat that most of the numbers I’m sharing will never be known to the MC with anything but the roughest degree of accuracy. The Hegemony is a state on the cusp of modernity, still struggling to make its population legible, and would probably still be at least a century or two away from developing an effective census bureau even if it weren’t in the process of collapse. Keeping reasonably accurate tabs on how many soldiers are in its army is just about at the limit of its capacity, and there are of course major challenges there too.
With that being said: on my current vision, the total Hegemonic armed forces across the whole continent number 1.4m, of whom some 273,000 are sailors in the navy. So the Phalangites compose less than 1% of the total Hegemonic population of almost 224m; an empire that wasn’t also trying to resource around 3m Alastors and their families could probably field a bigger army (early modern Europe had higher percentages even without benefit of Theurgy). But as it’s grown the Hegemony has had to devote much of its capacity for violence to keeping the 121m helot-and-drudge population from boiling over (plus the 21m free urban poor in the big cities).
A little more than half of the Phalangites’ total strength is stationed near the Halassur border (Moncesano and points east, including an actively contested area roughly the size of Wisconsin) and is periodically engaged in pacification, raiding, and (infrequent) Ward expansion operations. Another 10%-ish of the Hegemony’s military can be found in large concentrations near Aekos and the four provincial capitals. Most of the rest are in garrison towns near significant population centers. A few (1%) are at special garrisons elsewhere, e.g. the exceedingly rare Wardgates that aren’t closely adjacent to a major city.
When we look to the MC’s home province, per @apple’s question, the biggest garrison city is the one in the orbit of Grand Shayard, in Currechert, a camp that has become a small city in its own right. Around 15,000 Phalangites are based there. Nearby, much of the city of Osterport is made up of two garrisons a few miles apart that grew together: a naval base currently supporting 10,000+ sailors (on 60+ ships defending the Abhuman trade routes and the seas west of Scarthe) and a nearby Phalangite camp with 13,400 ground troops. Each of these three forces is headed by a myriarch, overseeing multiple turmarchs.
While the Osterport land garrison is in theory there to fend off an invastion by Abhumans, Halassur, and/or Corsairs (“should the Wards fail”), and does regular drills in preparation for that contingency, the abundance of soldiers in that bit of the Southriding is not unrelated to the risk of uprising among the 4m Shayardenes packed into the relatively small area around Grand Shayard and Osterport.
Elsewhere in Shayard, the Hegemonic Navy also has more than 20,000 sailors at their primary base of operations on Scarthe Isle, and over 8,000 in Aegre guarding the strait that protects access to Aveche (and thus to one of the major existing canal systems for food shipments to Karagon). The Aegre Strait, contrary to my earlier vision, is not crossed by a Ward; there are the rudiments of a great arch on either side which was left unfinished when the Ennearchs failed to muster the massive quantity of blood that would have been required for its completion.
There are no Phalangite garrisons in the Shayard Rim (yet); the nearest is in Vaulens, the 340,000 pop. city three districts deep into the Southriding. The force mustered against you in the summer would have been taken from Vaulens’ 9,700+ Phalangite garrison, which stands ready to support Alastors in keeping order across the whole Rim and the upper Southriding. (An area which also has a total population of around 4m [edit: yikes, sorry, more like 7-8m], but is less restive than the urban pressure cooker that is Grand Shayard/Osterport, and vastly less strategically significant.)
There are large garrisons (10-12k) in the 1m+ pop cities of Corlune and Rheges, and garrisons of a few thousand Phalangites in nearly all of the other non-Rim Shayardene cities named on the map, plus five or six that don’t appear on it.
Phalangite service is for a minimum of 10 years, and most non-nobles who are inducted into the army spend their whole life in it. Soldiers based in garrison cities tend to be accompanied by their families. Most Phalangites deployed to the Halassur border leave their spouses and children with comrades, so the garrison towns are also where most military widow/ers and orphans can be found. Many Phalangites are deployed long-term out of their home province, and it’s not uncommon (though of course vehemently discouraged) for Phalangites to marry different spouses in each province where they serve. Some are diligent in sending support back for all their families, while others leave them to the priests who coordinate help for widow/ers and orphans.
The military used to be significantly smaller, like the population of the Hegemony as a whole; both grew massively over the past century, as the Theurgic agricultural revolution really kicked into gear. Today Erezza is the most heavily garrisoned province, with sizeable garrisons in almost all of its coastal cities; by contrast, Nyryal has only about 60k Phalangites (mostly in Nyrnakan and Umri) and Wiendrj barely 15k (a function of its low helot population, lack of border threats, and rugged terrain). Both Nyryal and Wiendrj have a significantly higher rate of recruitment into the army, with therefore a high chance of being based outside their homeland; the garrison cities are among the most cosmopolitan places in the Hegemony.
Let’s stop there for now. Any questions? 
PS:
It hasn’t been mentioned, perhaps because literally no one in the gameworld is in a place to know that number or even make a reasonably close guess. My current estimate would be about 15% overall, which is a significant jump up after the invention of printing techne and a sporadic literacy campaign over the past couple of generations by the clergy… but that masks wild differences between social classes. The rural helot population’s rate, for example, is 0.5%.
15% is about half what Google tells me was the estimated literacy rate in Europe at the time of Gutenberg, but only a little lower than Nepal in 1981 (20%), and I think fits well with a caste-stratified society whose topmost elite has vastly more incentive than any society in our world to not promote mass education. (For the same reason, though, the Theurgic elite can’t explain in depth to religious functionaries why it’s a bad thing for them to teach more free folk to read the sacred writings, and there are obvious benefits to a more literate administrative class.)