Many articles online say that plant foods are poor sources of phosphatidylserine, except for white beans, which have 107 mg per 100 g.¹ ² ⁴ Honestly though, I think they might just be repeating a claim from Wikipedia, which cites "Souci SW, Fachmann E, Kraut H (2008). Food Composition and Nutrition Tables. Medpharm Scientific Publishers Stuttgart." I wasn't able to find this source freely available online. Examine.com mentions that "Phosphatidylserine (PS) is found in Soy Lecithin at around 3% of total phospholipids"⁵, citing https://www.ncbi.nlm.nih.gov/pubmed/18846580.
I haven't been able to find any (reliable) sources that say which kind of white bean is being referred to here: is it navy beans, cannellini beans, great northern beans, runner beans, or marrow beans? There are some that say navy beans,³, but I believe that information is derived from the Wikipedia article on phosphatidylserine, plus some speculation based on what the writer of the article thinks "white bean" refers to.