Telephone connection in US city on reflection is a joke! (3-5)
I believe the answer is:
one-liner
'a joke' is the definition.
(I know that one-liner is a type of joke)
'telephone connection in us city on reflection' is the wordplay.
'telephone connection' becomes 'nile' (I am not sure about this - if you are sure you should believe this answer much more).
'in' indicates putting letters inside.
'us city' becomes 'Reno' (city in Nevada).
'on reflection' shows that the letters should be reversed in order.
'nile' inserted within 'reno' is 'renileno'.
'renileno' reversed gives 'ONE-LINER'.
'is' is the link.
Can you help me to learn more?
(Other definitions for one-liner that I've seen before include "Pithy joke" , "Quick gag" , "Terse joke" , "Short joke - witty remark" , "Flat, smooth" .)