It is a pretty easy decision for Phillip. He will not let Mulan and Aurora die for him, especially since he just saved his true love. He isn’t afraid of dying. Mulan and Aurora will take care of each other and that is what is important. They will comfort the other in their grief. He takes his own comfort in that fact.
He means it when he tells Mulan and Aurora that he loves them. Mulan was his life for twenty-eight years and Aurora is his one true love. That means everything to Phillip and he can’t ever forget that. Mulan got him through the hard times when he lost hope. Aurora is the woman he’s loved since they were young and their parents forced them to talk. He just regrets he was not able to save her earlier, before the cruse took effect. And Phillip will forever be grateful that Mulan helped him to find Aurora after everything they had been through together.
He wants to do right by Mulan and Aurora. He just hopes they’ll forgive him for this eventually. He hates that it’ll happen in front of them, however.
Phillip doesn’t have any regrets as he dies.