There are people in Holland named Spyksma so it's hardly an anglicization though Spijksma is far more common. This is one of many variants as shown at
http://www.meertens.knaw.nl/nfd/detail_naam.php?naam=Spijk. As far as I can tell from
http://www.meertens.knaw.nl/nfd/detail_naam.php?naam=Spijkman, it denotes a person from a place named Spijk, one of which is in Friesland as you can see at
http://geonames.nga.mil/ggmagaz/geonames4.asp.