Specious excuse before phone message (7)
I believe the answer is:
pretext
'specious excuse' is the definition.
(I've seen this before)
'before phone message' is the wordplay.
'before' becomes 'pre' (prefix meaning 'before').
'phone message' becomes 'text' (I've seen this in another clue).
'pre'+'text'='PRETEXT'
(Other definitions for pretext that I've seen before include "Insincere excuse" , "Reason put forward to conceal the true one" , "Fictitious excuse" , "Ostensible reason" , "False reason, guise" .)