You can take the bus to “Vijfhuizen-Expo” for the western side of the Polderbaan. Though still have to walk about 2km. Busline 300. This line also stops at Schiphol Plaza.
https://goo.gl/maps/c7CnhrS46bicvcu26
For the approach to the center runway, you can go to busstop “Hoofddorp Hoofdweg 271”. One stop further is “Hoofddorp Vijfhuizerweg” which is near the taxiway towards the polderbaan. Busline 161 and 192. Neither line stops at Plaza. Line 192 is your easiest option by taking one of the many buslines to the bus terminal at Schiphol Noord.
https://goo.gl/maps/iYsbVchbVr7Qqg1c8
https://goo.gl/maps/EzLyDsg4VvHfJFso9
This website has maps of each individual busline, which might be usefull.
https://moovitapp.com/netherlands-101/l ... iType=line
Another website to check is
www.9292ov.nl which is a routeplanner that combines all public transport in the Netherlands. Just type where you want to go, and the site tells you which train or busline(s) to take, and how long the walk will be from the nearest buss top.