a.) Install the PhonePe APK
b.) Connect your Phone through your desktop/laptop. Please check if the developer options are on by following the below steps.
Go to :
System settings → Developer options → On
c.) Enable transfer files in USB debugging options.
3.) Enter chrome://inspect/ in the Chrome browser
You will be able to see the details of the device connected as shown in the below screenshot.
4.) Open the website URL from PhonePe APK. How to do the same can be found here.
You will be able to see the option on the chrome browser to inspect the details.
You will be able to inspect the network calls of the website inside the chrome browser and will be able to debug the flow.