The 1N4007 eliminates one of the detections because it becomes conductive (=0.7V) when current flows from its anode to its cathode so the opto only has 0.7V between pin 2&1 which is (should be) less than its min Forward voltage: no detection for this half of the sinewave. My point was: 0.7V is not far from the ~0.8V temperature sensitive threshold shown fig.1 page 3 that I mentioned post #61 so a unidirectional opto is safer.
BTW, if the only thing you want is phase sequence, you don't need a virtual ground and
the drawing post #52 should do but with the diode between pin 1&2 (antiparallel).
Virtual ground is necessary if you need zero crossing detection too.
The drawing from @JohnLincoln is the right one for zero crossing detection.