This challenge for developers

Are you able to code a complete working web application using just your smartphone? For the backend functions, it seems easy to do because backend involves crud operations + a data storage system. For the frontend, you may need to see how your web app looks like on a computer screen. You, of course, can emulate this with your smartphone.
I am Challenging developers to build a complete web application using a smartphone only.
Do you want to take the challenge?