Both Uses of

phase
in
The Throne of Fire

Change comes in phases, Ma'at and Chaos, Chaos and Ma'at.†
Chpt 21 *

phases = periods of time or stages during the development of something

Meanwhile, Ra played happily with his toys while the light servants flittered around the deck in agitation, apparently sensing that our journey was reaching a critical phase.†
Chpt 21

Definitions:

(1) (phase as in: a critical phase)
a period of time or a stage during the development of something
(2) (phase as in: she's going through a phase)
a period of time when someone exhibits unusual behavior
(3) (phase as in: phased out over three years)
make a change gradually (phase in = gradually add; phase out = gradually removed)
(4) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

More specialized and less common senses of the word are found in astronomy, physics, chemistry, and zoology. Consult a comprehensive dictionary if you wish to see those. All senses have to do with stages or periods of time.