The stress is placed on a syllable as far away from the end of the word as possible. Within reason of course. The Greeks decided that it would not be aesthetic to put the stress on any syllable further than 2 removed from the back, antepenult was fine, anything else was undesirable.
So what about καλεῖ , φιλῶ ? Last syllable is long, acute stress on syllable before, so why circumflex on last? See contractions. καλεῖ is actually καλέ ει , last syllable long, acute on penult. Which, if pronounced quickly, turns automatically into καλεῖ . Try saying it yourself and you'll see.