This isn't one of those crackpot claims. Phosphine is detected in significant quantities. It's difficult to make, and harder still to keep around.
This suggests that either there's a way to create Phosphine that is utterly beyond our imagination right now, or there's a life form in this band of Venus's atmosphere.
The first (chemistry we don't understand) is always a possibility, but it would be really, really weird.
The second (life in the atmosphere) isn't as insane as it might sound. There's a band in Venus's atmosphere where the hellish conditions of the surface (crazy heat, for starters) have toned down enough that life similar to what we know might be able to survive.
This article/video doesn't even begin to get into the next question...if it is life, how did it get there? Local evolution? Seeding from Earth, Mars or other?
This is not proof of life, but we don't know of any other explanation.
I'm really pleased with the tone set by the researchers. Not "WE FOUND LIFE", but "um, we're seeing this, it could be caused by life, we've checked out everything we can think of, can somebody please tell us what we missed?" Science at its best. :-)