Fill shelf (5,3)
I believe the answer is:
flesh out
'fill' is the definition.
'shelf' is the wordplay.
I cannot really see how this works, but
an anagram of 'shelf' is 'flesh' which is located in the answer.
The remaining letters 'out' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
(Other definitions for flesh out that I've seen before include "Substantiate" , "better explain?" , "vegetarian slogan" , "Elaborate - fatten up" , "Make or become substantial - sounds vaguely carnal" .)