I owned a PH-1 for over a year, and tried a number of tubes in it. The third tube (5687) is certainly important. My favorite was a Raytheon. The 12AX7 is equally important. My favorite there was a 1950's Mullard ECC83 long-plate.
I trust Dave's ears, and I certainly didn't try as many vintage 12AX7's in this unit as he did. Mullards were surprisingly uninspiring.
Like Dave, I had great success with the Raytheon 5687's (replacing the JAN Philips tubes the unit is supplied with).
I haven't priced Raytheon 5687's in the past year, but they were very cost effective at the time, and would therefore constitute low hanging fruit while you ponder the price of vintage 12AX7's.
The cryo'd 12AX7's that Aydn builds these phono stages with are surprisingly good.
Thom @ Galibier