The Phantom's main goal was to teach Christine to sing and marry her. Secondary and because of those motivation he sought to control who sang and keep his box, he did so through murder and extortion. On top of that keeping up the illusion that he was a ghost and staying hidden seemed to be his goals.
Very little if any of that is something the Polar Express could do. Even if his main job was to keep the Opera's audience enthralled. That's not something the Polar Express can do at the Opera House itself and stealing the Opera's audience isn't going to help with that goal.
The Phantom basically built the underground catacombs by himself and traveled the world building palaces, he has ties to national leaders. On top of a history with traveling shows, that traveled in northern Europe. So he's got experience with the cold, with massive logistical undertakings, and financiers if he needs them.
Remember the tracks existed separate from the Polar Express. So the Opera Ghost could just follow them.