Keeps in phase (3)
I believe the answer is:
has
'keeps' is the definition.
(keep can mean to have or possess)
'in phase' is the wordplay.
'in' indicates the answer is hidden within the clue.
'HAS' is hidden within 'phase'.
(Other definitions for has that I've seen before include "suffers from" , "Possesses or owns" , "Contains" , "Eats" , "Owns, holds" .)