Turn Table Cable Length

What imhifman said, short run to phono amp, longer interconnect. Keep in mind, the signal coming out of the cart is very low output and after 2-3’ (maybe shorter) the signal is degrading. Get your phono pre close if you can. 

Preferable to have a shorter length from turntable to amp and longer interconnects or speaker cables. If tt is your only source than move your amp together.
G

Your cartridge is MM/MI or MC? 

If you have a moving magnet cartridge this is a really bad idea as the added cable capacitance is going to really screw up the high frequencies.
You can get an inexpensive phono stage, very small and put it next to the table then as mentioned above run long interconnects from it to your amp. It is still not ideal but a bunch better then running long turntable cables.

If you are talking about a distance between the tonearm and the phono stage of 20 feet, that is a very bad idea regardless of what type of cartridge you will use, but it is an especially bad idea for a low output moving coil cartridge. Can you figure out some way to place the phono stage close to the turntable, within 3 ft ideally?And then it would be more acceptable to run a long cable from the output of the phono stage to your line stage. This is not just audiophile fussiness. A 20 foot phono cable will seriously degrade your listening pleasure.