heedem,
Phase angle is the term we use to describe the relationship between the input (swashplate tilt angle) and the ouput (tip path angle) for a dynamic occurence. It is literally the difference in rotation angle between the place where the swashplate tilts and the place where the rotor ends up tilting. People who build helicopters call that angle Gamma.
The guys seem to have a great deal of confusion over this, especially Lu, who asks that plaintive refrain, "Where did the 18 degrees go?" The 18 degrees is the difference between his mythological wish that phase angles are always 90 degrees, and the reality of the robbie's rotor head, where the phase angle is 78 degrees. If you subtract the real phase angle (78) from Lu's erroneous wish (90) you get the 18 degrees, and you confuse Lu.
The rotor is actually a dynamically tuned device, where the blades resonate in the flap axis. By resonate, I mean that the blades oscillate up and down in flapping at one full cycle per revolution of the rotor. A swing resonates at a specific frequency, and the child learns to lean back at exactly the same timing as the resonant frequency, so the swing applies the child's energy very efficiently during the resonant cycle. That is why a weak child can pick herself up to such heights while swinging. It is alo why the cyclic can so powerfully move the massive rotor with so little force. The rotor wants to flap to help you!