What model is the phono preamplifier?
Doing what you propose will often and perhaps usually be fine, but it depends on the output impedance of the phono preamp (the lower the better), the capacitance of the cable (the lower the better), and the characteristics of the shielding in the cable. Susceptibility of the phono preamp and the main preamp to ground loop issues (which is generally unpredictable), and whether the interconnection is balanced or unbalanced, can also sometimes be relevant factors.
Regards,
-- Al
Doing what you propose will often and perhaps usually be fine, but it depends on the output impedance of the phono preamp (the lower the better), the capacitance of the cable (the lower the better), and the characteristics of the shielding in the cable. Susceptibility of the phono preamp and the main preamp to ground loop issues (which is generally unpredictable), and whether the interconnection is balanced or unbalanced, can also sometimes be relevant factors.
Regards,
-- Al