Both Uses of

phase
in
Wuthering Heights

My confessions have not relieved me; but they may account for some otherwise unaccountable phases of humour which I show.†
p. 236.5 *

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

'What new phase of his character is this?' exclaimed Mrs. Linton, in amazement.†
p. 81.7

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.