Drivers get done in an order, this machine was likely left out for a longer time than others due to the fact the 10.9 driver is fully seemingly functional in 10.10 where some other devices 10.10 would not allow them to be installed. Most people just install the 10.9 driver and print.
The only differences between 10.9 and 10.10 is that Bidirectional ability is closed down in 10.10.
I am not an Engineer and have nothing to do with the driver developers by any means, but I did find a Phaser 3040 on the internal Xerox LAN and installed the 10.9 driver on our test Mac running 10.10.3 just now without any issue and successfully sent a test job to that printer. I just couldn't verify the output since I have no idea where that printer is, meaning someone, somewhere just got an odd job printed.