Both Uses

phase
in
Wuthering Heights
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'What new phase of his character is this?' exclaimed Mrs. Linton, in amazement.†
p. 81.7
My confessions have not relieved me; but they may account for some otherwise unaccountable phases of humour which I show.†
p. 236.5 *

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)
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.