This is most likely a diffraction pattern from the phone’s display, not a defect in your camera.

A smartphone screen is made of a very fine 2D grid of RGB subpixels. That regular grid can act like a diffraction grating, splitting and spreading light into colored patterns. When your DSLR photographs the screen at certain angles, distances, or focus conditions, the pixel array can produce a visible rainbow-like artifact.

So the source is the phone screen itself. Your lens and sensor simply recorded the effect; they usually aren’t the cause. The visibility of the pattern depends on the screen technology, pixel density, shooting angle, and magnification.

In short: it’s a normal optical interaction between the camera and the display’s pixel structure, similar to photographing other very fine repeating patterns.