Hi Irkin...
Long before I knew I had ADD I lost stuff all the time. Somehow I figured out that repetition helped create habits to help me. For things like keys, wallet and cell phone, each of these items can only go in a very few specific locations. For instance, my keys can only be in my left pocket, car ignition, kitchen drawer (I have a cubby in there where I place my keys the Second I get home. Repetition is important, so when I get home, I come in, set my laptop bag next to the kitchen cabinet, put my keys in the drawer, then go on with whatever business I have to attend to.

You can do the same thing with your phone. Cradle it in the car, pant pocket or belt holster and when you are not using it, always put it there, not on the table or counter... I know it sounds stupid, but if I sit my phone down where it does not belong, I stare at it and think of where it needs to be, finish what I'm doing and put it back where it should go.

With my ADD, repetition / structure / simplicity are key. I need as much as I can have on auto-pilot, so I can try to remember all the other stuff.

Good luck