Hi alexrat1996,
Thanks for reaching out in Apple Support Communities. I understand you'd like to know why you see a shine or reflection when you shine a light on the speaker in your iPhone. I can see why you'd reach out about this; I'd like to help. You're correct that you're seeing the reflection due to the mesh material that the speaker is made from and potentially structural components around or behind the mesh.
For further diagnosis of what you're observing, you can have the device examined at a nearby Apple Store or Authorized Service Provider: Find Locations
Best Regards.