Staff and volunteers each ringing one caller, primarily lawmen (6,8)

'lawmen' is the definition.
(police officer is a kind of lawman)

'staff and volunteers each ringing one caller primarily' is the wordplay.
I cannot really see how this works, but
'staff' could be 'office' (office staff is a kind of staff) and 'office' is found in the answer.
'one' could be 'o' (I've seen this in other clues) and 'o' is located in the answer.
This may be the basis of the clue (or it may be nonsense).