Army, perhaps on edge, professed loyalty that's insincere (3,7)
I believe the answer is:
lip service
'professed loyalty that's insincere' is the definition.
(lip service is an insincere expression of support)
'army perhaps on edge' is the wordplay.
'army perhaps' becomes 'service' (army is a kind of service).
'on' says to put letters next to each other.
'edge' becomes 'lip' (lip is a kind of edge).
'service' after 'lip' is 'LIP-SERVICE'.
(Other definitions for lip service that I've seen before include "Insincere offer to assist" , "Unreliable support" , "Insincere praise" , "Insincere support" , "It may be paid" .)