The reason you can make an unshielded cable work in a phono situation is that the cartridge is a pretty low impedance. Its hard for radiated noise to impinge the cable when such a low source impedance is present.
A further advantage is that unshielded cables have lower capacitance per foot, which is really helpful when dealing with the resonance that develops due to the cartridge inductance and the cable capacitance.
A further advantage is that unshielded cables have lower capacitance per foot, which is really helpful when dealing with the resonance that develops due to the cartridge inductance and the cable capacitance.

