I’d suggest simply giving it a wipe down every now and again, it’s like down to the environment the phone is being kept in but, also, it might be that the screen protector is attracting said dust. Not, a super issue though, just requires the odd wipe down every now and again! And, maybe think about getting a tempered glass protector - the pre-installed protector is useful but, I’d only ever suggest it been temporary while you look for another protector.
