Regarding the ESP32 web tutorials:
I did not findout the HTML code to be used on the smart phone.
Can you help me on this please?
You don’t need to upload any HTML code to your smartphone… Inside the Arduino sketch code it has the full web server that needs to be uploaded to your board.
If you look at the code lines (102 to 111), it has the full HTML page: https://github.com/RuiSantosdotme/ESP32-Course/blob/master/code/WiFi_Web_Server_Color_Picker/WiFi_Web_Server_Color_Picker.ino