Oooh, I'm not sure I agree with:
(2) During the IAS phase, drag is ALMOST constant, whilst TAS decreases. Thus the Rate of Descent is almost constant against a decreasing TAS, thus the descent angle constantly increases. Rate of Descent, whilst almost constant, will decrease slightly as drag reduces as EAS reduces for the same IAS with decreasing altitude. This latter factor slightly reduces the rate of increasing descent angle, but only slightly.
For a given airframe weight the glide angle is pretty much purely dependent on IAS. TAS is a bit of a red herring in this discussion.
If you descend at constant IAS, your glide angle will stay the same throughout (neglecting things like change of wind/ISA deviation/fuel burn/changing idle thrust, etc.). As your TAS reduces, so will your ROD to compensate
but the glide angle stays constant.
Try it sometime in a real aircraft. Start a fixed IAS descent at, say 250Kts @ 40,000'; note idle ROD: it will be around twice what you'd expect at sea level because your TAS is about twice your IAS at that altitude. Your glide angle is fundamentally the same.