During the Japanese occupation, the Philippines Peso was replace with the Japanese Peso. All transactions in occupied areas had to be conducted in Japanese Pesos. At the same time in unoccupied areas there was used of Local Emergency Pesos. After the war the Japanese Peso was deemed worthless by the Allied . Which was unfortunate for those that were forced to used them. Prewar Pesos could be exchanged at Par and Local Emergency Pesos could be exchanged on a sliding scale. The stamp is from one of 2 large groups who collect them and tried unsuccessfully to force the Americans to exchange them for new currency.
Like all things paper money is only worth what someone else will give your for them.