Yours truly's on the phone, not going anywhere (8)
I believe the answer is:
immobile
'not going anywhere' is the definition.
(I've seen this before)
'yours truly's on the phone' is the wordplay.
'yours truly's' becomes 'im' (I'm).
'on' says to put letters next to each other.
'the phone' becomes 'mobile' (I've seen this before).
'im'+'mobile'='IMMOBILE'
(Other definitions for immobile that I've seen before include "Not going anywhere" , "Static" , "Incapable of motion" , "Not able to move or be moved" , "Can't travel" .)