Every 2-3 weeks remove the phone from casing, wipe with damp cloth to remove dust…or whenever I switch casing..

I dont recommend to wash even with water, just wipe it with damp clothes... a friend of mine washed his iphone 12PM under sink for a quick 5 secs flush, voided the warranty under water damage, and paid a hefty amount to repair it... so unnecessary and sad for him..