Hello vimalmuthusamy,
Let's test that behavior in another location, if you haven't already done so. That should help to further rule out wireless interference as a contributing factor: Resolve Wi-Fi and Bluetooth issues caused by wireless interference - Apple Support
Should that behavior still persist, does this happen during other tasks, such as listening to music or watching videos?
Have you had the opportunity to test your iPhone with any other headphones? How about testing your earbuds with another device? This will help us to isolate the behavior to either your iPhone, or the ear buds themselves to avoid unnecessary troubleshooting steps.
Let us know, and we'll keep moving forward from there.