Keeps in phase (3)
I believe the answer is:
has
'keeps' is the definition.
(I've seen this in other clues)
'in phase' is the wordplay.
'in' says the answer is hidden in the clue.
'HAS' is hidden in the letters of 'phase'.
(Other definitions for has that I've seen before include "suffers from" , "Possesses or owns" , "Contains" , "Eats" , "Owns, holds" .)