Hii there,

Hope you are doing well, as per your query I suggest you to operate on a desktop for the choice filling of JOSAA, because there are hundreds of option which you can easily place in desktop. But you can also work on mobile phone, there is no such compulsion of using any particular desktop while choice filling and further procedures. For more doubts please refer here:

https://engineering.careers360.com/articles/josaa-registration-and-choice-filling

All the best!!