"Arcadium’s current annual lithium production capacity across a range of products including lithium hydroxide and lithium carbonate is 75,000 tonnes lithium carbonate equivalent2, with expansion plans in place to more than double capacity by the end of 20283."
Can't compare with one a developer and the other already producing. However from a planned production point of view, Arcadium plans to reach around 150ktpa by 2028 and Phoenix around 70 or 75,000tpa in 2029. By that basis alone, as crude as it is, maybe Phoenix could reach half of Arcadium's valuation when it starts producing, ie. around US$3.8bill hopefully in around 4 years. Of course by then, lithium might be back in deficit and all lithium stock valuations might double or better what they are now. That doubling would get Phoenix's valuation up to closer to its estimated NPV.