The difference between phono cable and interconnect cable is SHIELD , not a ground wire. Do you understand why 99% phono cables are shielded? The signal from phono cartridge (especially MC) is much lower than line level signal from any other component. Without shielded cable you can hear a radio signal in your speakers or noise and hum when you connect it to your tonearm/turntable with MC cart.
Some interconnects are shielded, but most if them are not shielded and using them instead of phono cable is bad idea.
As for the ground wire you can use any thin wire (it will not affect sound quality) between turntable ground terminal and phonostage ground terminal if needed.