Elevated command is quite difficult to execute (4,5)
I believe the answer is:
tall order
'quite difficult to execute' is the definition.
I can't judge whether this definition defines the answer.
'elevated command' is the wordplay.
'elevated' becomes 'tall' (I am not sure about this - if you are sure you should believe this answer much more).
'command' becomes 'order' (order is a kind of command).
'tall'+'order'='TALL ORDER'
'is' is the link.
Can you help me to learn more?
(Other definitions for tall order that I've seen before include "I want a skyscraper built by tomorrow" , "Demanding work" , "Difficult demand" , "Unreasonable demand" , "you'll be lucky!" .)