As one's despicably mean, small tips for servants materialise (2,5)
I believe the answer is:
en masse
'as one's' is the definition.
(both can mean as a group)
'despicably mean small tips for servants materialise' is the wordplay.
'despicably' indicates anagramming the letters (despicable implies wrongness).
'small' becomes 's' (abbreviation - e.g. clothes size).
'tips for' indicates one should take the final letters (tip can mean the end of something).
The last letters of 'servants materialise' are 'se'.
'mean' with letters rearranged gives 'enma'.
'enma'+'s'+'se'='EN MASSE'
(Other definitions for en masse that I've seen before include "In a group U altogether" , "All together as a group" , "As a body (Fr.)" , "as a bunch" , "in concert" .)