Phaeton's redesigned as one-seater carriage (8)
I believe the answer is:
stanhope
'one-seater carriage' is the definition.
(type of carriage)
'phaeton's redesigned' is the wordplay.
'redesigned' is an anagram indicator.
'phaetons' is an anagram of 'STANHOPE'.
'as' is the link.
(Other definitions for stanhope that I've seen before include "vehicle" , "old-fashioned conveyance" , "Light horse-drawn carriage; Nineteen across (anag.)" , "It may have only two wheels" , "carriage that has seat only for one" .)