There is a sticker that can be attached to the phone case and will light up when there is a phone call. What's the name of this sticker?

A sticker with a luminous mobile phone is called a lightning sticker.

Lightning itself does not need batteries, and its working principle is that light energy comes from electromagnetic waves. When the mobile phone sends a signal to the base station, it will send out a strong electromagnetic wave. According to the electromagnetic theory, when electromagnetic waves meet the antenna in the air, they will generate voltage and current in the middle section of the antenna. The flash sticker is actually a receiving antenna, which converts the electromagnetic wave signal of the mobile phone into voltage and current, thus emitting light.