Would it make sense to equip a phalangite with a longer sword for battle in looser formation? Normally a phalangite would have a pike (sarissa), shield and a short sword that can be used in a packed formation if necessary. But could it reasonably be justified to keep a longer sword for flexibility in action in broken terrain or would that be too encumbering and/or an expense that is unjustified? If you need more context to the question feel free to ask.
Are you talking about something longer, but short enough to be used with one hand? Are you looking for historical accuracy or just something logical based on the story?
For historical accuracy Bronze Age swords were typically not longer than 80 cm; weapons significantly shorter than 60 cm are variously categorized as short swords or daggers. I would stay with the standard load. Those would be the weapons the person was most familiar with. When combined with a shield, the short sword will often disappear from the opponents sight. So the blow can easily come from an unexpected angle. In melee combat like that Era had skill and not weapon length would be more of a deciding factor. Some points to consider, but in the end it is your story.
Yeah, a one handed weapon to allow the phalangites to keep fighting also on broken ground and not "do a battle of Pydna". I will consider it. But as I think I mentioned above its that I wonder what steps one might have taken to allow phalangites to perform also when fighting enemies who could and would fight on broken ground. Leaving the phalangites to sit on the side line seems like a massive waste to me.
The Greeks used hoplites as a concentration of force. I would suggest you look at the Greek battles in the middle east. Xenoph and the March of the ten thousand is a good place to start. The cultural doctrine of the Middle East is for raiding. This contrast should give you a base for what you are looking for.
