I'd argue you're not commenting on any specific language at all here, but rather the sheer size of the community/user base for a given language.
Yes and no. A larger community will for sure help with filling in knowledge gaps, but those gaps stem from the documentation not covering something in enough detail.
Maybe it's just me but whenever I read Elixir, Phoenix or Ecto's docs I can't really relate to them. It feels like they are written for a completely different type of person and very rarely do they focus on practical applications of something. Most of the docs feel more like a reference guide to a library's API and if you're lucky you'll get an example or 2, but there's not enough context written around it to figure out how to apply that to your specific problem. That and the docs are rarely linked to a meaningful result when Googling for stuff.
It's a much different world than Python, Ruby and PHP IMO.
Again, though, reading between the lines, it sounds distinctly like your complaint is with the ecosystem and its maturity, not anything to do with the language itself. "No, it's not that!" you say, as you go on to mention three very, very mature languages with massive ecosystems that I do agree are a very different world.
Python, Ruby, and PHP are all great! It's difficult to even think of a language that has a better wealth of guides and resources out there than any of those three (with the exception of maybe JavaScript). Elixir and Erlang, two fairly niche languages that are the actual topic of conversation for this overarching thread, simply aren't comparable in that regard.
Elixir inherited some of the Ruby history and contributors, and has some of the same strengths.
My only experience before Phoenix was Django, and I have to say, even though it took a little while to wrap my head around Phoenix, it was about the same time it took to get my head around Django. Once I did, I found Pheonix to be more expressive and exceedingly productive.
However, after a year of developing and learning elixir I am dropping it. Just did not like it in the end, I prefer other languages and everything I like about Elixir was basically Erlang.