how to change hotspot login form, that wifi client input a phone number in login form and it output in some_file.txt with date/time/phone_number ?
You can only do this if you use external authentication, you would have a webserver somewhere, and there you would have a simple registration form that would gather the entered credentials into a database, and then allow the user to use internet.
Some examples:
https://wiki.mikrotik.com/wiki/Manual:Customizing_Hotspot#External_authentication
We don’t have specific examples for the external server part.
Use DMA Radius Manager for this option even more results