When was the last time you cleaned your smartphone, maybe have never which is due to the reason you don't want it to get damaged.
It is good to have your smartphone cleaned especially the screen and if you can slide your phone and take a look at the screen, you will notice that it is covered with dirts which might be from the dust(major case), your dirty fingerprint on the screen etc.

It is required to always clean your smartphone at least once in a day and if you check whenever you clean your smartphone screen, it's so easy(smoothly) to slide your finger across it than when it's covered with dirts or dust all over it. So if you want to clean your smartphone, please turn it off or put it on sleep mode.

How to clean your smartphone screen:

If you want to clean your smartphone screen, it is advisable to use a microfiber cloth which is very soft to clean up the dirts on your screen. Please do not use soft tissue paper, any how cloth or your towel which can cause scratches on your device especially if it's not made of gorilla Glass.

Then if the dirt is a stubborn one and can't be easily cleaned with a dry microfiber cloth, just dampen the microfiber cloth or any soft cloth similar to the microfiber on a distilled water and clean it up. Please do not try to pour a little bit of water on your
screen even if it's water resistance. Some people try to use a detergent or alcohol to clean off those stubborn dirts on their screen but this is not advisable please.

Clean the case:

Things have changed as most smartphones we have is touchscreen(very few with physical keyboard) and some are non removal. If you a blackberry user with physical keyboard, there’s a way of cleaning your Blackberry phone when it gets dirty by first of all turning off your device and removing the battery. After that get a cotton bud or put a cotton wool on a slightly mouth pin object, dip it on a diluted spirit or any alcohol and then rub it slowly and gently on your keyboard. If you are afraid not to get the spirit into your phone please use ordinary water.

For removable phones when you remove the battery use the cotton bud with it dipped in spirit or any alcohol or ordinary water and gently rub it around the battery area to the camera lens etc. Please after you cleaned an area, dry it up immediately so as to avoid any liquid entering into your phone.
If you have a case clean it too with a spirit or any alcohol with a cotton wool or cotton bud.

http://www.zpykios.com/2015/10/clean-your-smartphone-screen-and-body.html?m=1

Thanks for the information
I'll try this on my Phantom 9