I have to write, as a chemist, that amounts of phosphine in the atmosphere of Venus, however small, must be regarded as dubious. In the presence of tiny amounts of oxygen, the gas is spontaneously flammable, forming phosphorus pentoxide as a white smoke, and water vapour. We know that photolysis of oxygen-containing compounds by short-wave UV radiation can produce oxygen radicals in the atmosphere of Venus, so there is certainly going to be a short lifetime for any phosphine. By the way, I often demonstrated its flammability to my A level classes, though I don’t recommend it as a home experiment. You take a tiny piece of white phosphorus, which of course can no longer be bought, and cover it with a few cc of very concentrated NaOH solution, and heat gently it in the fume cupboard. Attach a delivery tube and after a few moments the apparatus will emit beautiful white smoke rings from the end, as each bubble of phosphine combines with the air. No need to add that caustic soda is dangerous, and white phosphorus even more so!