I believe “phyto-” refers to chemicals produced by plants that are molecularly similar or act in a similar way in human/animal cells as other chemicals, for instance estrogen.
Tribulus wouldn’t go under the definition as a phytoandrogen (if that even is a definition), as it allegedly increases testosterone indirectly by stimulating LH production - not by acting directly like testosterone or any other androgen.
You would think that since there are plant hormones structurally similar to estradiol, there would be some similar to testosterone. Maybe the limited chemicals produced by plants cellular respiration and photosynthesis is why there might be none? Maybe some pro-hormones actually are phytochemicals? I don’t know. It would be cool if someone more knowledgeable could comment on this.
By the way, I did a search on “phytoandrogens” and found this: http://aquaculture.ocean.org.il/ija/57/57-1_62-66.pdf
The article mentions androstenedione as a phytoandrogen.