Auto speaker switch while calling !

Hello bgbikram,

Since this started happening have you restarted your phone? If not, let's give that a try. It may be a simple step but it can resolve many issues like yours.

Restart your iPhone - Apple Support

Let's also check an Accessibility setting to ensure one of those settings isn't causing the phone to automatically go to speaker.

Settings > Accessibility > Touch > Call Audio Routing.

Ensure that it is set to Automatic and not Speaker.

Let us know if you have any questions.

Thank you for using Apple Support Communities.

Take care!

Hi bgbikram,

Do you have the phone up to your face when this occurs? We want to make sure the proximity sensor is detecting you're holding your iPhone to your face.

Based on the troubleshooting that has been completed up to this point, your best bet will be to Get Support directly from Apple from here on out. You can use the link here to get started.

Regards.