A man makes numerous phone calls trying to negotiate his own safety while travelling to his gangster boss to confess his failure, finally having to settle for saving his family from revenge.

I see a little Midnight Run type opportunity here.

Would benefit from a ticking clock.? He has X hours to do whatever.

Being responsible for bringing an undercover cop into their organisation a gangster travels to see his boss while making a series of calls trying to rescue the situation finally settling on just being able to save his family.

>>>negotiate his own safety

More to the point, the stakes are his life and that of his family.? From the FADE IN, isn't that's what he's fighting/negotiating for?

After failing his mission, a criminal tries to negotiate his own safety while traveling to confront his gangster boss, and ultimately rescue his family.

Admittedly my longline isn't the greatest, but I think you need to to re-word this so it streamlines it.

The protagonist needs a descriptor other then "a man". Who is he? Did he fail his mission because he's having a crisis of conscience? Or is he simply a gangster that failed? What's redeeming about this man/gangster that makes us want to root for him?

Why does he need to confess his failure? ?His boss would already have gotten word that he failed his mission, no? ?I think it's better if the boss knows so the whole script they're at odds, and he's FORCED to go confront his boss because his family's lives are at stake, and he can't simply disappear or walk away.

No one would "settle" for saving their family from revenge. That should be the driving action that makes him step up. ?People may be criminals, but the love of family if the strongest motivator of all.

Have you seen Locke? A great film with Tom Hardy. The whole film takes place in one car, on one journey, told through phone conversations he has on the road. Your idea made me think of this.