Mobile in a jacket pocket finally stolen (5)
I believe the answer is:
agile
'mobile' is the definition.
(thesaurus)
'a jacket pocket finally stolen' is the wordplay.
'a' becomes 'article' ('a' is the indefinite article in English).
'jacket' says to hollow out the word (remove centre letters) (the letters worn by the word as a 'jacket' are use).
'pocket' means one lot of letters goes inside another.
'finally stolen' becomes 'gil' (I am not sure about this - if you are sure you should believe this answer much more).
'article' with its middle removed is 'ae'.
'ae' enclosing 'gil' is 'AGILE'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for agile that I've seen before include "Dexterous" , "Nimble on the feet" , "Spry - energetic" , "Nimble, lithe" , "Limber" .)