Here's the introduction to the song from the U. Utah Phillips songbook, Starlight on the Rails And other songs (Dream Garden Press, Salt Lake City, ©2011, by Duncan Phillips. (page 123)

PHOEBE SNOW
I was standing outside an empty yard in Chicago on my way to Bloomington, lllinois. I saw one of those beautiful Gulf, Mobile and Ohio freight trains, made up and ready to head south, with the red and maroon GMO boxcars with the gold stripe around them. A train like that is irresistible to me. I figured it was probably going to St. Louis to be rehumped and some of the cars sent west, because it was hauling a lot of Burlington, Denver Rio Grande, Santa Fe, and Union Pacific.
The car I got on was an old Phoebe Snow boxcar from the Erie Lackawanna in Pennsylvania. At the time the name Phoebe Snow conjured up the face and form of anybody I'd ever been in love with, so I made up this song for want of anything better to do. l crossed the state and sang the song first in the big jungle camp in Danville. It wasn't until I got back to Chicago that Richard Marko, a Chicago performer, told me who Phoebe Snow really was.
The Erie Lackawanna was the first line to use anthracite coal, which meant that their trains were soot-free—you could ride their passenger runs without getting a lot of soot in your clothing. To advertise that fact the railroad used a cartoon character, a beautiful woman all dressed in white, with long white gloves, a white hat, and a white purse. She would be talking to somebody across the aisle about how clean it was to ride the Route of the Anthracite. Her name was Phoebe Snow.
She was famous all over the country for many years. About 1963 the Erie Lackawanna discontinued their passenger runs and took Phoebe Snow off. But you can still find some of those old boxcars if you look around a yard.