I have just went through this same comparison on my own system. IMO, both of the mentioned units, Phonomena and GCPH, are equally as good. I feel that sound quality, depth, staging, over dynamics are great on both, these are both a great upgrade from my Creek 15.
As far as hum or hiss on the GCPH, I did have a slight hiss problem in my unit, not hum. I would say in my system it was more of a gain issue on the GCPH. The secondary gain on front of unit had to be turned up to much for proper gain, this is due to a 2W per ch amp and passive volume control. I called PS Audio and I did perform a transformer tuning, per their instructions. This did help my hiss slightly but I think this would be more of a solution for transformer hum instead. Based off of this, I have kept the Phonomena and problem solved. I feel that with an active pre-amp, this would not have been an issue on the GCPH. Both units have a ton of adjustment and sound awesome for their price range. One more quick note, the battery operated power supply is a bit more transparent on the Phonomena with a better noise floor. IMO, in a larger room than mine with a little less efficient speakers (100db, full range, single point source are what I'm using)with multi-drivers and passive crossovers, both units should perform very close. Considering what you can buy either unit for used here on Agon, try them both and re-sale what you don't use.
As far as hum or hiss on the GCPH, I did have a slight hiss problem in my unit, not hum. I would say in my system it was more of a gain issue on the GCPH. The secondary gain on front of unit had to be turned up to much for proper gain, this is due to a 2W per ch amp and passive volume control. I called PS Audio and I did perform a transformer tuning, per their instructions. This did help my hiss slightly but I think this would be more of a solution for transformer hum instead. Based off of this, I have kept the Phonomena and problem solved. I feel that with an active pre-amp, this would not have been an issue on the GCPH. Both units have a ton of adjustment and sound awesome for their price range. One more quick note, the battery operated power supply is a bit more transparent on the Phonomena with a better noise floor. IMO, in a larger room than mine with a little less efficient speakers (100db, full range, single point source are what I'm using)with multi-drivers and passive crossovers, both units should perform very close. Considering what you can buy either unit for used here on Agon, try them both and re-sale what you don't use.