Although I do not intend to verify this, I am convinced that you cannot change how iOS places the navigation bar in the field when the keyboard is displayed in Safari. I have tested several web applications (especially gmail) and it also exists.
In iOS application development, this panel, which Safari places above the keyboard, is a view that the application does not create where content is created or accessed (your web application).
Unfortunately, the only way I know is to create your own native iOS application and upload it to the web application. (See Sample Mail Application).
source share