It is ONLY the Cartridge/Tonearm that needs to be grounded. No separate ground wire is needed from Preamp to Amp
A typical Phono Cable has an integral ground wire
Separate Ground Connectors (various types of wire attachment terminals) exist at both ends/both devices for the ground wire of the Phono Cable. Labeled GND, or something like that.
ANY ’real’ Phono input receives the cartridge’s low level un-equalized signal and a ground connection must exist, typically adjacent to the ’phono’ input (not always adjacent, it can be somewhere else on the back of the input device).
Other ’non-real’ Phono Inputs exist, but they are simply ’named’ Phono, for the convenience of front selector input names. They are ’line level’ inputs, requiring the cartridge’s low level and un-equalized signal to have been converted to line level elsewhere. No ground wire is needed for those ’non-real’ phono inputs.
Typically, if you see the rear panel, and a pair of rca jacks exist labeled phono, if there is no adjacent separate ground connector, it is a ’non-real’ ’named’ phono input.
Careful research of any device is required to determine if the device contains a ’real’ phono input of the cartridge’s low level signal or a ’non-real named’ phono input of an already equalized/boosted to line level signal strength.