100% agree. If there's a choice between a small amount of pollution vs a large payoff to cut carbon emissions, it's definitely a good idea. For instance, any pollution that comes from the production of solar panels and batteries is probably something we should accept, because the payoff is a large cut in emissions.
But we're not talking about pollution directly in the cause of cutting emissions here. We're talking about separate pollution which is avoidable and has nothing to do with cutting emissions.
The point is, if we use all of this phosphate to make better batteries it would be great and have a good impact on emissions, but most of it will be spread on the ground and let run into rivers because that is the main industrial use of phosphates