How to solve weird whitish shadow on my dad' iPhone 5s?

Dear all.

I bought an iPhone 5s brand new for my father almost 2 years ago (In Indonesia Apple reseller still sell it brand new until last year), and the phone worked pretty well until last week.

Immediately most of the display had whitish shadow, showed by this photo:

I think he barely dropped his phone so I’m bit confused about the problem, though he works as building material provider so bit dusty environment is prevalent.

Do you think the solution is to replace the whole LCD? or any simple tricks can deal just fine?