The crescent-shaped artifact is most likely lens flare: an internal reflection inside the phone’s lens system. It is a much dimmer, displaced copy of the Sun, so it can show the eclipse shape against the darker sky.

The actual image of the Sun is far brighter and overwhelms the phone camera’s sensor. Smartphone cameras have small, fixed-aperture lenses and limited exposure control, so the Sun easily saturates the sensor and blooms/glows, wiping out edge detail. That’s why the main solar disc may look like a blown-out bright blob instead of a crescent.

In short:

• The Sun image is too bright, so the sensor clips and loses the eclipse detail.
• The flare/reflection is much dimmer, so its crescent shape remains visible.
• The artifact exists because no lens is perfectly free of internal reflections, especially when pointed at an extremely bright light source like the Sun.

Be careful photographing the Sun; use proper solar filters for safe and usable results.