Is about to get up but flags (6)
I believe the answer is:
irises
'flags' is the definition.
(I know this)
'is about to get up' is the wordplay.
'about' indicates putting letters inside.
'to get up' becomes 'rise' ('rise' can be a synonym of 'get up').
'is' going around 'rise' is 'IRISES'.
'but' is the link.
(Other definitions for irises that I've seen before include "Plants with sword-shaped leaves" , "Eye membranes or showy flowers." , "Parts of eyes or flowering plants" , "Coloured membranes in eyes, or showy flowers" , "Is sire in favour of flowers?" .)