so earlier today i started up a new world, accidently forgot to set it to creative, opened it to lan, set myself to creative, derped arround, then left for work. its been about 10.5 hours since i left and i never shut the game down. As the sun comes up from over the horizon in game i hear a wierd sound, and look at discord as i had just switched voice channels thinking it was that, but then nothing. a few seconds later i hear some wierd sounds again (mind you i havent played very much 1.13 or above, as i play alot of moddeda). so i fly around looking for it and i see phantoms, burning, and theres about 30 of them... mind you ive been in creative for about 10 hours at this point. 

tldr: it would seem that phantoms spawn naturaly when your in creative, which is wierd and im pretty sure is a bug.