Provided glass on a mobile (2,4,2)
I believe the answer is:
as long as
'provided' is the definition.
(both can mean if certain conditions are met)
'glass on a mobile' is the wordplay.
'mobile' indicates an anagram.
'glass'+'on'+'a'='glassona'
'glassona' with letters rearranged gives 'AS LONG AS'.
(Other definitions for as long as that I've seen before include "for the time" , "On condition that - (" ___ your arm")" , "Provided" .)