The fix (Jim Boyce, Tom Lehmann, Steve Thomas and Don Woods):
Place a six-sided die in the center of the board, initially set to 6. A phase shift occurs only when both dice rolled have numbers equal to or greater than the number showing on this die. If only one of the dice rolled has a number equal to or greater than the number showing, the phase doesn't shift but the central die is reduced to its next lowest value (6 to 5, 3 to 2, etc.).
When a phase shift occurs, roll the center die to determine what game phase it has shifted into. Then place the central die back to 6 and finish resolving the game phase shift normally.
Note: Double 6s will always result in a phase shift while other doubles may or may not (but still always have their normal effects on rumors).
This change smooths out how often phase shifts occur just enough to allow the various strategies (gas stations, oil drilling, refineries, mixed) an equal chance to work, while still keeping a fair amount of uncertainty in the game.