I use coax for my RCA cables, including phono cables, and the woven copper sheath that surrounds the dielectric carries the ground and is soldered to the outside of the RCA plug. Most phono preamps sum the L and R grounds plus the preamp's chassis ground and my XB has the cartridge grounds summed at the RCA jacks. In addition, the T-bar, tonearm and top plate are also tied to the cartridge grounds and therefore to the preamp ground via the cable.
I've used standard RG-59 coax for a variety of cables (component video, subwoofer, phono, digital coax, etc) with 75-ohm connectors but wasn't satisfied with its use for phono. I thought I was getting some induced hum but the cable was pretty stiff and sometimes made connections difficult so I'm doing something different now. I'm currently making RCA cables with Mogami 2965 twin coax and Neurtrik Rean NYS-373 RCA plugs. The 2965 is very flexible and the NYS-373s are nice plugs. On the back of the AR bases I built I installed Neutrik NF2D jacks. All seem to work well together.