It comes with a slim metal piece with adhesive on one side, which you remove the adhesive cover and then stick to the back of your phone or a phone case. But if you use any of the Otter Box cases, then you can just as easily leave the adhesive cover on the slim metal piece and place it between the two case pieces and it will still hold very well to the mount. I have an iPhone6s that it works very well, but larger phones such as 6S Plus or 7 Plus are heavier so placing the metal magnet between the two case pieces could lessen its ability to hold on to the mount