Unless I’m mistaken, the input impedance of your phono preamp is 47,000 Ohms. This means an increase in impedance from a long length makes no difference.
Shielding is the next thing. I have a 1.5m length phono cable. If that shielded phono cable crosses a power cord, I get a slight hum. Therefore make sure your long phono cable doesn’t get too close to a power cable.