The 6 phases of this "Larson scanner" are given by 6 logic sources. The diodes prevent short between logic sources (wired OR gates) and prevents the capacitors to drain trough the logic sources which gives some afterglow for the bulbs.
Any number of phase is possible with the same number of logic sources and diodes.
This idea with LEDs: http://everycircuit.com/circuit/4955755392532480
