I’m posting on behalf of Annabel Hanson.
The University of Hull has developed a very simple method for measuring phosphates. They have created a paper device that just needs to be dipped into a water sample. It then changes colour in the presence of phosphates (and they are working on nitrate device). They also have a mobile app (called RiverDip, which you can download for the Apple or Google app stores) which allows users to record the measurements.
If you want to get in touch with them email Mark Lorch on M.Lorch@hull.ac.uk