Discovered phoney saint is lacking guile (6)
I believe the answer is:
honest
'is lacking guile' is the definition.
I can't judge whether this definition defines the answer.
'discovered phoney saint' is the wordplay.
'discovered' means to look at the middle letters (dis-covered - outer letters removed).
'saint' becomes 'st' (abbreviation).
The middle of 'phoney' is 'hone'.
'hone'+'st'='HONEST'
Can you help me to learn more?
(Other definitions for honest that I've seen before include "Direct" , "Fair and just, not crooked" , "Sincere, upright" , "Open and truthful" , "Not cheating, just" .)