Genuflect when talking to Armstrong (5)
I believe the answer is:
kneel
'genuflect' is the definition.
(I've seen this before)
'talking to armstrong' is the wordplay.
'talking' shows a homophone (sound like).
'to armstrong' becomes 'neil' (Neil Armstrong).
'neil' sounds like 'KNEEL'.
'when' is the link.
(Other definitions for kneel that I've seen before include "Rest on hassock" , "Adopt position for prayer or submission" , "Kowtow" , "Genuflect" , "Crouch down" .)