Phoneys besetting weak revolutionary? (6)
I believe the answer is:
fawkes
'revolutionary?' is the definition.
(Guy Fawkes)
'phoneys besetting weak' is the wordplay.
'phoneys' becomes 'fakes'.
'besetting' is an insertion indicator.
'weak' becomes 'w' (physics symbol as in W-boson).
'fakes' going around 'w' is 'FAWKES'.
(Other definitions for fawkes that I've seen before include "Guy --, conspirator" , "Guy -- (November 5)" , "Guy -- (Gunpowder Plot)" , "Gunpowder plotter" , "Guy . . . . . . burned in effigy on Nov 5th" .)