(Any of various synthetic thermosetting resins, obtained by the reaction of phenols with simple aldehydes and used to make molded products and as coatings and adhesives. Also called phenolic resin )
As you can see, the word describes what the gasket is made of and not it's insulating ability. Spacers made of Phenolics require a gasket on both sides to get a good seal. Teflon will slightly conform to the two mating surfaces and create a gasket-free seal. Teflon is much easier for the mechanic and has similar, if not better qualities than comparable phenolics.
You can make your own Teflon Spacer. Pre-made insulating spacers are usually only available for the typical domestics and Hondas..
I have used this multiple times in the past: ".125" x 12" x 24" Teflon(r) Virgin Grade Skived Sheet ". If your project requires more of a "spacer" than .125", just pick the thickness you want and the instructions are the same. Make sure you have room and bolt length available to use the thickness you are ordering.
It insulates very well and has an operating range of -400 to 500F. Low heat expansion, easy to cut, soft enough that it will seal well between two surfaces. I used a ball point pen to indent/trace the gasket (intake manifold, throttle body, etc.gaskets) into the Teflon, a drill, small project hack saw, and a razor blade to smooth out the cuts.
Completed Intake Manifold Gasket and a Partially Complete Throttle Body Gasket
Here is some info on different options
Good example of standard pricing for Teflon (choose "Industrial
Plastics - Sheet, Plate"):
Try an EBay search for Phenolics or Teflon to see if there are any deals on there.
Hope this helps you. I have been using a 10" Coping Saw and Drill to get the rough design and a thin project razor blad to smooth out the cuts and perfectly size the phenolic gasket. If you have access to a water jet cutter, that would be the best method.