Betting, using a pay-phone (8)
I believe the answer is:
wagering
'betting' is the definition.
('wager' can be a synonym of 'bet')
'a pay-phone' is the wordplay.
'a pay' becomes 'wage' ('wage' can be a synonym of 'pay').
'phone' becomes 'ring' ('ring' can be a synonym of 'phone').
'wage'+'ring'='WAGERING'
'using' acts as a link.
(Other definitions for wagering that I've seen before include "Betting" , "better operation" .)