I know for a fact that penis envy exists. Females have been slapping me in the face with it since I was six. While I wouldn't say that EVERY one of them has it, or has gone through it, they are a fair chunk of the female population. You'd just never know it from how often their posts online about the subject get erased. They also will get dogpiled on by feminists and their allies, white knights, goddess-worshippers, and the plain ignorant who have long ago swallowed western gynocentrism as some normal fact of life. This is why we will never have any truthful stats about it. There are a lot of people out there who have made it their cause to bury the very idea, and I'm sure they have their individual reasons for working toward this common goal. There will always be people who fear the truth so much that they will stop at nothing to force as many others to believe in the lie that they, personally, find so comforting.
It has gotten so vicious that the psychiatric community online has had to go underground on the subject. If you want to read papers written by professionals on the subject, you'll soon learn that they are safely locked away behind very expensive paywalls.
As far as the public at large is concerned, it is nothing more than the ramblings of an old druggie who lived in chauvinistic times. I hate when this topic gets derailed by antagonists bringing up Freud and some of his more outlandish conclusions. I'll give him credit for spotting the issue and naming it. But invoking Freud in any modern discussion of penis envy is like having a bunch of aeronautics engineers who are trying to improve fighter jet designs by invoking the Wright brothers' views on aircraft design. Sure, they got one up into the air, but if you look at their design, it's backward.
Little girl penis envy can be temporary, or last through a lifetime. If the latter happens, it often mutates into something else as she gets older, and understands that the best she can ever hope to accomplish is second-hand ownership of the actual organ. She transfers that childish desire into other pursuits that will color her life, for better or worse.
I could write a book on my lifelong observations of this issue.