Distance ET with a telephone box (8)
I believe the answer is:
alienate
'distance' is the definition.
(I've seen this in another clue)
'et with a telephone box' is the wordplay.
'et' becomes 'alien' (short for extra-terrestrial).
'with' says to put letters next to each other.
'a telephone box' becomes 'ate' (I can't explain this - if you can you should believe this answer much more).
'alien'+'ate'='ALIENATE'
Can you help me to learn more?
(Other definitions for alienate that I've seen before include "Estrange, disaffect" , "Arouse hostility" , "A Count, worked to unify Italy" , "Cause someone to feel estranged" , "Set against" .)