According to the "Sterbebücher" (death records) of Auschwitz, Philip van Kollem was murdered there on 20 August 1942. This date is different from the official date of death as determined by the Dutch Ministry of Justice after the war. For the time being, the website joodsmonument.nl, list only the dates of death, as published at the time in the "Nederlandse Staatscourant" (Dutch Government Gazette) by the Ministry of Justice.
Sterbebuch Auschwitz (death record)
Official death certificate nr. 277 for Philip van Kollem dated 8 September 1950 (after clicking the link, the website will open - just wait a few seconds and then scroll to the correct deed).