Why does my metal phone ring stand becomes iridescent, and turns back to normal after a while?
This is an interference phenomenon, more specifically interference of light between two thin layers with an air gap. Recall the beautiful soap bubble as an example. Whatever coating your have on this object gets very very slightly separated from the surface upon mild heating. This generates an air gap between two layers.

Iridescence is a different phenomenon, which is angle dependent in the sense that you see different colors at different angles.

If you have over heated an empty stainless steel frying pan by mistake, that also forms a interference pattern (purple tinge). This is because of an oxide coating on the surface but it is not reversible. You have to scrub it away.