One fearful of strangers smashes phone box with energy (9)
I believe the answer is:
xenophobe
'one fearful of strangers' is the definition.
'smashes phone box with energy' is the wordplay.
'smashes' indicates anagramming the letters.
'with' means one lot of letters goes inside another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'phone'+'box'='phonebox'
'phonebox' is an anagram of 'xnophobe'.
'xnophobe' placed around 'e' is 'XENOPHOBE'.
(Other definitions for xenophobe that I've seen before include "One fears or hates foreigners" , "One fearing foreigners" , "hating foreigners" , "One afraid of strangers" , "Person fearing strangers" .)