Need help in having a field in form (to select country based on mobile number)

I need to develop a form in which I need to have a field to select country based on mobile number entered by user.
Can someone help me with the this.

Sharing the design of form which needs to be done (this will give you an idea of my question, please see the image and help me out.)


Here is my site Read-Only: LINK
(how to share your site Read-Only link)