It doesn’t even need to be on a soft surface (bed/carpet etc) it would ignite most things, those batteries get so hot. We used to do training on how to cool them down if there was a fire on an aircraft - you’d submerge them in water (obviously not picking it up with your hand). They used to say put it in a metal tub of water because it might melt a plastic tub if it touched the sides.
Never leave your phone charging somewhere when you’re not nearby.