My set up is really simple. Turntable --> preamp --> speakers/headphones. The preamp itself is grounded; it has a 3-pin power plug and it has never been altered in any way.The phono stage, if I understand you correctly (I may not be very familiar with terminology), consists of two RCA-type input jacks (one is for the left channel, and another is for the right channel) and two RCA-type output jacks. No other jacks, just these four.
The preamp does have a grounding post, but I am not sure if it is "dedicated to the phono", although it should be, because turntables is what this preamp is made for. I tried grounding my turntable to this post, but it did not help.