When a country invades a neighbor using phosphorus bombs, they are giving open permission for phosphorus bombs to be used in their country as well. There should be no complaints from Vlad Puta if phosphorus bombs started landing in Moscow.
I know everyone wants Ukraine to take the "moral high ground", but when only one country is permitted to engage in heinous acts like this, it gives an extreme and unfair advantage to the offending country. If they win because of their advantages, it is worth it to them. The only way it becomes NOT worth it to them is when those horrific measures are recieved in return. Otherwise, why return fire in the event of a nuclear strike? The credible threat of suffering the same fate is how you stop the threat. Phosphorus bombs should be used on targets within Russia if we want any chance of them reconsidering the use of such weapons.