Thank you for using the Support Forum. You should be able to still add the printer on macOS using the built-in “Generic Postscript PPD”. You will not get all your features but you should be able to print.
Please consider contacting your support centre for further assistance.
I am an independent book designer. I purchased a Phaser 5550 and a Phaser 7760GX several years ago. (Ability to print 11 x 17 and occassionally 12 x 18 paper was an essential requirement.) Due to changes in the industry (impact of the Internet and ability of my clients to handle proof copies as PDF) resulted in much lower print volume than initially anticipated. (These printers replaced a Phaser 5500 and a very slow color laser printer that Xerox "took over" after acquiring the printer manufacturer.)
The LAST official Xerox driver for these printers support Mac OS X 10.10 (Yosemite). That driver was issued in 2014 and was replaced by by OS X 10.11 in 2015. The replacement OS X was not "friendly" with the Xerox Drivers. (Note the same driver worked both printers satisfactorily prior to 10.11.) Unfortunately, with 10.11, certain settings would "crash" the program attempting to print. (I understand that the driver would return a response that the software "did not expect.") These problems were most frequent with Adobe InDesign (like I said, I'm a book designer and typesetting is a major part of what I do.)
For a LONG time, Xerox stated that they "were considering" issuing an update. Aparently, the consideration resulted in a "not going to happen." So here we are 5 years later, fortunately OSX 10.15 doesn't seem as ruffled by the old drivers (crashes don't often happen) and Adobe Acrobat is able to access most of the feaatrues of my printers without crashing.
I did PAY FOR a thrid party driver, that really supported HP printers, but sort of supported corresponding Xerox printers. Unfortunately, it proved to be unreliable and did not consistently support all functions properly.
So, I'm willing to pay (a reasonable amount) for an updated driver that fully supports these "legacy" printers. Indeed, I've "shopped" the Xerox web site and not found a replacement that is as good or better than these existing "low mileage" printers.