It’s a jeu de mots that won’t be in any dictionary: in French, we have embouteillage, meaning a traffic jam, but containing the word bouteille. In Antiquity, bouteilles were amphores, so they re-used the construction for embouteillage to make amphore + -age = amphorisage.

The word does not really exist in French, it’s just made up here. Nobody will understand what you say if you go around talking about amphorisage for traffic jams – well except maybe you could pass for somebody who has read Astérix, if people recognize the reference.

Be on the lookout for jeux de mots in Astérix, it has quite a few (chaque été les Ibères deviennent plus rudes is one of my favorites).