How to track the location of the phone?

Question

Mobile devices

There is only a phone number and the ability to send a link to the user, say, leave it on VK or Instagram.

In theory, if you give the user a link and he will go to it or download something by installing a hidden application for surveillance, but what kind of application?
Or how to write your own?
There should be some samples on git, but what to look for?

Answer 1

until the user clicks to install the application (a tick in the settings is an unknown source at least), until he gives permission for geolocation - nothing will happen, even in the browser it asks for geolocation - user permission is needed.

Answer 2

Well, only if he does not poke himself - allow geolocation ...
on iOS, this is not realistic at all in my opinion