Instrument that measures current pollution described by new phrase (11)
I believe the answer is:
seismograph
'instrument that measures' is the definition.
'current pollution described by new phrase' is the wordplay.
'current' becomes 'i' (symbol for electric current).
'pollution' becomes 'smog' (smog is a kind of pollution).
'described by' indicates putting letters inside (to describe can mean to form an outline).
'new' is an anagram indicator.
'i'+'smog'='ismog'
'phrase' with letters rearranged gives 'seraph'.
'ismog' going into 'seraph' is 'SEISMOGRAPH'.
(Other definitions for seismograph that I've seen before include "What detects such tremors" , "Tremor detector" , "Instrument for registering earthquakes" , "Earthquake recorder" , "Earthquake measuring instrument" .)