are phono cables different from regular rca's?

to go from a step-up amp (Hagerman, FET) into the the mm input of the phono preamp, it would seem that an rca-terminated "phono" cable would be indicated; it's outputting a signal essentially the same as a mm signal from a cartridge. Is a "phono" cable intended for such low-level signals preferable to a normal rca interconnect, in this application? Are they constructed differently?
No. Just use any interconnect you have or like.
Well, you can indeed use any interconnect if you don't mind the hum. Best that it be shielded.
Most interconnects are shielded. I've never had a problem
with hum because of the interconnects I've used. I would not use an unshielded cable (such as PBJ) for this application.
It's all relative to the system and surrounding environment. I use all unshielded IC's (my brand) and have zero noise/hum....dead quite in my system.
I have been using older Bettercable Blue Truth as turntable interconnects and switched out for a gold helix IC from ELF Audio. The latter is unshielded and when deployed there was significant and unpleasant hum. Switched back to the BT and all was fine (except I want more neutrality in my phono section). I will further experiment with shielded phono cables.