Ringtone volume automatically decrease
I have recently purchased iPhone 13 Mini, now facing a problem that when anyone call me, my ringtone sound loudly but after few seconds it automatically decreased. I have checked with all of my ringtone but found the same. Even I saw few tutorials and tried but didn't see any updates. My ringer volume taken max level and enabled Toggle but failed.
Please help me and thanks in advance.
iPhone 13 mini, iOS 15