GenLias has the marriage record for Philip Nathan and Judic Witteboon. It also notes that Philip Cohen is known as Philip Nathan:
Huw 13-06-1912 Amsterdam #reg.6D;fol.22: Philip Nathan 21 jaar g. Amsterdam, beroep Diamantslijper (Joseph Nathan, beroep Diamantslijper en Anna van Gelder) en Judic Wit…
In addition, a Jokos file (number 10775) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.