Is there any time limit in the List view of the iPhone Calendar app, beyond which we cannot make any entries? Can this limit be changed to something else than the 2 years set by by Apple?
There is no limit in the Calendar itself – you can 'zoom out' by repeatedly tapping the Back button until you're in a screen where each year takes up about a single page. Scroll down to e.g. 2027, and you can create an event in the distant future without problems:
The List view does seem to have a built-in limit of two years, which can't be extended by settings.