where we can by bus to foshan from guangzhou

To there, you can find frequent buses at local City Bus Station or Fangcun Bus Station.
From FS, there is no direct buses to reach Guzhen and you need to transfer at Xiaolan.
In many stations in FS such as Yuehai Bus Station and Gaoming Bus Station, you can find buses to reach Xiaolan. At xiaolan, you can take bus B1 to reach Guzhen.