Cellphones are not allowed to be used in the polls in WI. There are 2 reasons: 1) we don’t want voters taking direction from someone outside the polls when voting. 2) we don’t want people taking pictures of ballots being filled out.
That said, I think that every election worker ought to have the ability to record wrong doing at the polls whenever it happens. By the time you report it to the authorities, the perp is gone. Or (in the worst case) you may be dead.
Walk outside the polling site, call law enforcement and file a complaint against the person before they leave or try to get their license number. Would that work?