Sweatier when swimming, so to speak (2,2,4)
I believe the answer is:
as it were
'so to speak' is the definition.
(synonyms)
'sweatier when swimming' is the wordplay.
'when swimming' indicates anagramming the letters.
'sweatier' with letters rearranged gives 'AS IT WERE'.
(Other definitions for as it were that I've seen before include "Just like if really so" , "In a manner of speaking" , "Seemingly" , "Historically ungrammatical" , "you might say" .)