Returning it (the call) is wearisome (6)
I believe the answer is:
tiring
'wearisome' is the definition.
(thesaurus)
'returning it the call' is the wordplay.
'returning' is a reversal indicator.
'the call' becomes 'ring' (I've seen this before).
'it' in reverse letter order is 'ti'.
'ti'+'ring'='TIRING'
'is' is the link.
(Other definitions for tiring that I've seen before include "Boring" , "Causing weariness" , "Growing weary or bored" , "Wearisome" , "Becoming sleepy" .)