Are the Phaser models native RGB or CMYK? e.g. if I send a CMYK file will the Phaser convert it to RGB then back to its own CMYK?
The driver converts the RGB to CMYK and sends to the printer.
Some models can print pdf files directly, they can interpret RGB, all printers that can only print a print ready file are CMYK only.
In short, if you LPR a pdf from the command line to your printer and it works, it can interpret RGB, if it fails, it cannot.