Staircase feature miler Roger’s spoken of (8)
I believe the answer is:
banister
'staircase feature' is the definition.
(a staircase might have a banister)
'miler roger's spoken of' is the wordplay.
'miler roger' becomes 'bannister' (runner Roger Bannister, 1929-2018).
'spoken of' indicates a 'sounds like' (homophone) clue.
'bannister' sounds like 'BANISTER'.
(Other definitions for banister that I've seen before include "Rail beside a staircase" , "support at hand on flight" , "Support running alongside stairs" , "Staircase handrail" , "Staircase railing" .)