I think the main confusion with the Germans comes from a misunderstanding of what a "phalanx" is. A phalanx does not necessarily imply the use of pikes - it is simply a closely packed formation of men. There is, to my knowledge no reference to the Germans or the Helvetii using pikes or very long spears. Indeed, Tacitus says that the typical German weapon is a small, light spear suitable both for throwing and fighting hand to hand.
I would suggest that in both of these cases, the use of the word phalanx by classical authors does not imply a pike formation, but simply a closely packed formation of men using their shields to defend themselves, somewhat like the "scildweall" of later Germanic warfare.
One formation that is well attested among the early Germans is a wedge of infantry with the bravest and best armoured at the front.
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