Mobile phone’s cases yet to change for starters (9)
I believe the answer is:
neophytes
'for starters' is the definition.
('neophyte' can be a synonym of 'starter')
'mobile phone's cases yet to change' is the wordplay.
'mobile' is an anagram indicator (mobile can mean moving).
'cases' means one lot of letters goes inside another (forms a case around).
'to change' indicates anagramming the letters.
'phones' with letters rearranged gives 'neophs'.
'yet' anagrammed gives 'yte'.
'neophs' enclosing 'yte' is 'NEOPHYTES'.
(Other definitions for neophytes that I've seen before include "Newcomers" , "Novices" .)