[Q] Quality of the headphone jack on the MXP

In terms of 1. the sound output on the headphone jack (sound quality, output volume). How does it compare to other phones that you have owned? How does it compare to the iphones with the best headphone sound quality such as the iphone 4 or the iphone 5s.

and 2. build quality (is there an inner ring made of metal inside the jack ,completely flush with the metal contact part of the plug, to stabilize the heaphone plug?). Is the headphone plug stable enough when plugged such that it will withstand prolonged usage?