On call, not every girl: certainly no aristocrat (7-5)
I believe the answer is:
working-class
'certainly no aristocrat' is the definition.
(aristocrats are upper-class)
'on call not every girl' is the wordplay.
'on' becomes 'working'.
'not' is a deletion indicator.
'every' becomes 'all' (similar in meaning).
'girl' becomes 'lass' (lass is a kind of girl).
'call' with 'all' taken out is 'c'.
'working'+'c'+'lass'='WORKING-CLASS'
(Other definitions for working-class that I've seen before include "Blue-collar" , "Proletarian" .)