You can think of electrical phases like any other kind of wave: maybe like shaking a slinky. The power plant sends the phases downstream to consumers, and once it leaves the factory it doesn't know what consumers do with it (beyond detecting voltage drops, etc.).

So the grid doesn't need to balance it, no.

And from the receiving end's perspective, power will be exactly one phase out of sync if the cables differ in length by 5000 km. I'm assuming that isn't really a problem people have to worry about, but my background is in physics and not engineering (i.e. maybe there's some industrial applications that I'm not thinking of).