To the extent that fashionable couch breaks regularly (2,2,3,2)
I believe the answer is:
in so far as
'to the extent that' is the definition.
(both can be used to qualify a statement)
'fashionable couch breaks regularly' is the wordplay.
'fashionable' becomes 'in' (in can mean fashionable or trendy).
'couch' becomes 'sofa' (synonyms).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternate letters of 'breaks' are 'ras'.
'in'+'sofa'+'ras'='IN SO FAR AS'
(Another definition for in so far as that I've seen is " To the extent that".)