Phases no different, just relative (7)
I believe the answer is:
stepson
'relative' is the definition.
(stepson is a kind of relative)
'phases no different' is the wordplay.
'phases' becomes 'steps' (I've seen this in another clue).
'different' indicates anagramming the letters (letters placed in a different order).
'no' is an anagram of 'on'.
'steps'+'on'='STEPSON'
'just' acts as a link.
(Other definitions for stepson that I've seen before include "Relation, not by blood" , "Child from a spouse's former marriage" , "Subdues" , "unrelated issue" , "second family member" .)