Thank you Valerie!
Actually , I understand from your answer that there is no way anymore, be it on Phoenix or V3, to tweak one's own environment settings to achieve personal special environment effects, as it was in the past. One can only choose between the region settings ( if any), or between uploaded ready-made settings, if I am correct.
This seems to me a HUGE step backwards! Is there another way to access to the advanced sky or water menus, with their atmosphere, lighting, clouds tabs, or is it absolutely impossible from now on? and is there anybody here who would wish to join me to ask Linden Labs to consider making it available again?