A reinforced company selected from breacher squads of the Imperial Fists Legion, the Phalanx Warders are charged with the defence of the capital flagship, the Phalanx. They are therefore kitted out for boarding actions - both defensive and offensive against enemies. But clearly, they are also of good utility on a highly packed out game board with plenty of terrain features.
The strengths of this unit in comparison to the more typical breacher squad may not be too obvious at first. But one has to factor in the Imperial Fists rules, and their rite of war to see the big benefit. To be clear: a 3+/5++ T5 squad running around in large numbers is going to be a pain for many enemies. Equally, that 3+ armour save is not the best. And for the points value, it may be more prudent for the Imperial Fists players to think about terminator squads instead. Therefore, I would only council running these guys in specialist Imperial Fists builds, or if the controlling player wanted something very fluffy and well suited to the Imperial Fists.
That said, there is a good deal of flexibility available for what kind of builds to utilise with the squad. Given they can sacrifice their (BS5) bolt guns for power axes, there are a number of "modes" in which to build them: for close ranged fire fights, or for pure melee, for objective sitting, or perhaps something in-between. Don't forget, with the increased initiative if they get charged, they can hold their own against enemy squads nicely. But it may not be enough.
I see their 3+ armour save as being the biggest deterrent for taking this squad, followed by their points costs. They will die like standard marines. And terminators are categorically more attractive for the power gamer I think.
As with other Imperial Fist squads, they're slow. They will need some kind of transport (land raider!) to carry them around, or otherwise, attach an apothecary to the squad and use them to sit on an objective for the game.
Below, I look at a number of ways to build this squad, some more suited to melee and close combat than others (who are more ranged).
10 Phalanx Warders, legion vexilla, sergeant with power fist and artificer armour (295 points)
This is the baseline squad. The price is already up there, and you can now see why I think baseline terminators are just better, even if there are 10 members in this squad. Add flamers to taste for objective sitting squads.
20 Phalanx Warders, legion vexilla, 4 thunder hammers, 5 power axes, sergeant with Solarite power gauntlet, artificer armour and melta bombs (570 points)
Very expensive here as each upgrade costs per model (and not for the squad). Take these guys in a Spartan land raider and happy hunting to you.
10 Phalanx Warders, legion vexilla, 2 plasma guns, 5 power axes, sergeant with artificer armour, plasma pistol and melta bombs (380 points)
A smaller, more plasma orientated version of the above squad. I contend 10 terminators with combi-weapons are strictly better at this level. Replace the plasma with breacher charges if you like?
I want to like this unit. Genuinely, I really do. The models are fantastic. But the rules prove to be over-costed for what they do and they're taking up a valuable fast attack slot. Take terminators instead to be honest. Or if you do take them, realise that they are a good fluffy choice, team them up with a land raider, the Imperial Fists rite of war, an apothecary and be happy with them.