Select the most appropriate phrasal verb to fill in the blank.

The driver very subtly ___________ the traffic violation he committed.

The correct answer is ironed out.

Explanation:
The phrasal verb "iron out" means to resolve, settle, or eliminate differences, difficulties, or problems. In this context, it refers to the driver subtly settling or resolving the traffic violation they committed (for example, by reaching an agreement, clarifying a misunderstanding, or fixing the issue on the spot).

Let's look at why the other options are incorrect:
- "Ironed through" is not a standard English phrasal verb.
- "Ironed in" is not standard English in this context (though "iron in" can refer to pressing a crease into fabric, it doesn't mean resolving a problem).
- "Ironed aside" is not a standard phrasal verb.