Why is there echo on my iPhone 15 video calls?

I got my iphone 15 2 or 3 weeks ago and since then when making a video call, the receiving side hears their own voice and says there is an echo. There is no problem during the normal calls or when I use headphones on video call. Could it be a hardware problem or is there something I should change in the settings? Anyone with the same problem?

[Re-Titled by Moderator]