Poem's outstanding when read aloud (3)
I believe the answer is:
ode
'poem's' is the definition.
(ode is a type of poem)
'outstanding when read aloud' is the wordplay.
'outstanding' becomes 'owed' (as in an outstanding debt).
'when read aloud' shows a homophone (sound like).
'owed' sounds like 'ODE'.
(Other definitions for ode that I've seen before include "Poem expressing noble feelings" , "Sung poem" , "poetry" , "A poem celebrating person or event" , "(Railway)system" .)