Association of workers on telephone get old teaching (8)
I believe the answer is:
tutelage
'teaching' is the definition.
(I know that tutelage is a type of teaching)
'association of workers on telephone get old' is the wordplay.
'association of workers' becomes 'TU' (abbreviation for trade union).
'on' is a charade indicator (letters next to each other).
'telephone' becomes 'tel' (short for telephone).
'get old' becomes 'age' (to age is to get older).
'tu'+'tel'+'age'='TUTELAGE'
(Other definitions for tutelage that I've seen before include "Protection" , "Tuition" , "Schooling" , "Training" , "guidance" .)