What purpose does the wicker fence serve?

The correct answer is - protection of the cargo.

The wicker fence on the ships of the Phoenicians had the purpose to protect the cargo. Since the sea waters are not always calm, and very often, out of nowhere, a storm can emerge and contribute to bigger waves, as well as rocking of the ship itself, the Phoenicians invented a simple trick, and that was the wicker fence. With it on place, the cargo was safe on the boat, and it was not able to slip away and be lost in the sea.