Try phoning Irish town overlooking last event (9)
I believe the answer is:
triathlon
'event' is the definition.
(sporting event)
'try phoning irish town overlooking last' is the wordplay.
'phoning' indicates a 'sounds like' (homophone) clue (as it might sound on the phone).
'irish town' becomes 'athlone' (town in Ireland).
'overlooking last' means to remove the last letter.
'try' is a homophone of 'tri'.
'athlone' with its last letter removed is 'athlon'.
'tri'+'athlon'='TRIATHLON'
(Other definitions for triathlon that I've seen before include "Swimming/cycling/running event" , "Sporting contest comprising swimming, cycling and running" , "Contest involving swimming, running and cycling" , "Athletics event" , "Athletic contest in three events" .)