The weakness of the phalanx is that you can be outflanked; it's really hard to turn a long pike to address an opponent not in front of you. I would imagine that having cavalry to protect your flanks would make it a lot more effective.

The swiss didn't ise a classic wide phalanx formation but a more densely packed square formation. Their pikes would stand out in all directions as a sort of hedgehog. Only the corners would be a weaker point. The flanks and rear would be well covered by pikes.

The pikes would generally stand only in one direction at once, and their drills had diagonal forms, so the corners would not be a weak point.

When people think pikemen, they think of very static formations, with little mobility. This is true of a lot of historical pike units, but the Swiss pikemen are the opposite of it. They drilled as small companies of ~100 men, and they were so successful because they made mobility as an unit into an art. A swiss pike block was drilled to change facing in seconds, and they liked to charge pikes levelled at near running speed. Many a condottiere got their last surprise when they were at the last stretch of their charge against an exposed flank or rear of a swiss block, and suddenly all the pikes rise, everyone turns, all the pikes come down again, and the swiss start charging the would-be attackers like madmen.