Why can you not catch phanpy on Pokemon SoulSilver?

You are mistaken! You can actually catch Phanpy in Pokémon SoulSilver.

Here's how:

* Phanpy is found in the Ilex Forest. You can find it in the grass patches throughout the forest.

* Phanpy is a relatively common encounter. It's not as rare as some other Pokémon in the game.

So, you definitely have the chance to catch Phanpy in Pokémon SoulSilver!