Q: When I pick up a call, my phone keeps vibrating for a second a two. After that I am not able to here the caller. When I put my phone on speaker mode I could hear the caller. Even if I convert it to normal mode I am able to here thereafter.

Hello anuragkr40,

Thank you for using the Apple Support Communities. Let's see what we can do to get your iPhone's receiver working the way it should!

First, please start by following the instructions in this support article:

If you can't hear a person on a call or voicemail or if the sound isn't clear on your iPhone - Apple Support

If the issue is still occurring after these steps, we need to isolate the problem to either a hardware issue or a software issue.  To do this, you'll need to restore the iPhone and set it up as a new device.  Since this will erase all the content on the iPhone, be sure to create a backup first. Backup instructions can be found here:

How to back up your devices using iCloud or iTunes

Once you have a backup, restore the iPhone using these steps:

Use iTunes on your Mac or PC to restore your iPhone, iPad, or iPod to factory settings - Apple Support

Be sure to set up your device as a new device rather than restore the device from the backup.  Once the iPhone is set up as new, test and see if the issue remains.  If it does, then the best option would be to have the iPhone checked out by an Apple Authorized Service Provider.  You can find the closest one by looking here:

Find Locations

If the problem is no longer occurring, then go ahead and restore the backup using these instructions:

Restore your device from an iCloud or iTunes backup - Apple Support

If the problem starts again, this would indicate that there is something being loaded from the backup that is causing the issue.  If that happens, you would need to set up as new again, reinstall the apps you'd like to use, and re-add content that you need back onto the iPhone.

Have a great day!