Recently I had bought a floor mat at the auto parts store. This floor mat is rubber with 3/16" thickness all around, the thickness varies from 1/16" to 3/16". For some reason my smartphone texting features work better when the smartphone is placed on this rubber mat.
In this picture the floor mat has been marked with a Sharpie Silver pen. This type of pen works well on a black surface. I marked a rectangle which is about one inch larger than the smart phone itself.
After cutting the outline with heavy duty scissors, the finished product looks like this.
Fin.