It appears we have potential signs of life on our neighbour.
"The presence of PH3 is unexplained after exhaustive study of steady-state chemistry and photochemical pathways, with no currently known abiotic production routes in Venus’s atmosphere, clouds, surface and subsurface, or from lightning, volcanic or meteoritic delivery. PH3 could originate from unknown photochemistry or geochemistry, or, by analogy with biological production of PH3 on Earth, from the presence of life. Other PH3 spectral features should be sought, while in situ cloud and surface sampling could examine sources of this gas."From the abstract of Phosphine gas in the cloud decks of Venus - Nature Astronomy ISSN 2397-3366 (online)
In other words, we know how it's made and we've eliminated all the known non-biological options. We either have life (a known source of the molecule) or a previously unknown chemical process.
Either way, exciting news. :)