It's a complicated subject, as theoretically limiting the charge current might minimally help to reduce heat generation when charging. However, all iPhones will reduce the charging current as it approaches getting full, so that's not an issue where it's going to be forcing current into the battery when it could potentially overheat.
It's generally something that's not worth overthinking. It works and faster charging is supposed to be more convenient. Worst case is maybe it shaves off a tiny bit of longevity. However, Apple's ratings for battery longevity take everything into account including using the fastest charging.