My iPhone 7 is rated IP67 which means it is splash, water and dust resistant. However, I’m not sure they tested the dust resistance by mounting the phone on the handlebar of a motorcycle ridden at high speeds in dusty conditions. I say that because dust managed to enter my phone and got stuck to the camera sensor. I was told that there was no way to clean the dust from the sensor (🙄) and I had to replace the entire camera. The technician said that the dust most probably entered through the pores of the front facing microphone.
So I came up with this solution. A piece of paper cut to size, folded in half and tucked inside the phone case. When I mount the phone on the handlebar I unfold the paper so that it covers all front facing openings.