One's in a phonebox, somehow rejecting foreign callers? (10)
I believe the answer is:
xenophobia
'rejecting foreign callers?' is the definition.
(dislike of foreigners)
'one's in a phonebox somehow' is the wordplay.
'one' becomes 'I' (Roman numeral).
'in' is an insertion indicator.
'somehow' indicates anagramming the letters.
'a'+'phonebox'='aphonebox'
'aphonebox' with letters rearranged gives 'xenophoba'.
'i' inserted within 'xenophoba' is 'XENOPHOBIA'.
(Other definitions for xenophobia that I've seen before include "intolerance" , "Excessive fear of foreigners" , "Fear or dislike of foreigners" , "Hatred of the foreign" , "for blocking of foreign connections?" .)