How to reverse phase on a cartridge?

OK thanks for that. I should have mentioned that it is a phono preamp only.
I don't hear anything odd, or thin sounding, so perhaps that indicates that all is OK.

Jmcgrogan2, please note that the only piece of equipment that inverts phase is the OP's standalone phono pre-amp, therefore, the OP only option is to switch the cartridge lead without affecting other sources in his system.

is out of phase noticeable?

Yes it can be. The sound will appear to come from no specific location i.e. no defined centre image etc.

Please note that not all source material is recorded with the same phase, therefore, it becomes a bit of a crap shoot.

On top of everything else, who is to say what is "correct" phase? Only the listener who can perceive a difference when phase is shifted by 180 degrees at all frequencies, by any of the maneuvers desribed above. Yet, as far as I know, there was no particular phase orthodoxy observed in any recording studio or in LP or CD production. I have read that even on any one LP, the phase can differ from one cut to the next. Further, crossovers and other unavoidable elements in the electronic pathway also alter phase in a frequency-specific manner. Further, further, acoustic phase is altered by room reflections. And finally, you say your phono stage sounds "fine". With all that taken into account, I would say "fuhgeddaboudit". Surely, as an audiophile, you can find something else to fret about. I know I can.

My bad Brf, you are correct. I should have read the post with my glasses on. ;)