Q: Phone app in iPhone 5S not responding

Hey m_varghese, 

Welcome to Apple Support Communities.

If I understand correctly, the Phone app isn't responding on your iPhone 5s. Take a look at the article below and try the general troubleshooting tips that it provides, which can resolve issues with any app.

If an app you installed unexpectedly quits, stops responding, or won’t open - Apple Support

Restart the app

Close the app and open it again.

 

Restart your device

Turn your device off and back on.

If the issue persists, try restoring your iPhone as shown here:

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

Cheers.