Unerringly Phidias captures character in carving (5)
I believe the answer is:
glyph
'character in carving' is the definition.
(I've seen this before)
'unerringly phidias captures' is the wordplay.
'captures' indicates a hidden word (the answer is trapped within the clue).
'GLYPH' is hidden within 'unerringly phidias'.
(Other definitions for glyph that I've seen before include "Sculptured symbol; frieze groove" , "Sculptured character" , "character in carving" , "Sculpted symbol" .)