I had a White machine that was new in 1966 that came with a circle attachment. I remember trying it out, but didn't have a use for it at the time. It seems to me that it was nothing more than a little pin that attached point up in various holes on the machine bed, and had a cap of some sort to keep the fabric from popping off. I wish I'd kept that old machine, but when I inherited my mom's slightly newer Elna in 1986, I had the crazy idea that I only needed one sewing machine.
The beauty of this phone book method is that you can make bigger circles than you could with a device that's attached to the machine bed. I believe I would use some duct tape to attach the phone books either to the machine or the table to make sure my circle didn't turn into an ellipse. Just the vibration from the machine could possibly cause it to slide.
You can buy circle attachments that apparently fit various machines. Here's a youtube video demonstrating a couple of different ones.
https://www.youtube.com/watch?v=4WO7nwIKdnI