1. First you have enable "Developer mode" on your mobile device. (Different device might be different)

"Settings" -> Click "Build Number" 7 times.

2. Enable "USB debugging"

"Settings" -> "Developer option" --> enable "USB debugging"

3. Connect your device with your laptop

4. Open Chrome on your laptop, and visit:

chrome://inspect

5. Now you are able to open emulator on your laptop, the actions was sync between laptop and device.

You can inspect any components by using dev tool as usuall.

For IOS, please check:

https://github.com/google/ios-webkit-debug-proxy

[Tools] Using mobile device for debugging your mobile web site