(for pure speculation and reflection)
Dear D., Well, he might have as the "specifying" part of his name Zangs-dkar Slob-dpon, or Zans-dkar Bla-ma. I don't know about any Tibetan biography (I should check TBRC before saying that), so the information I know of comes from the literature about Csoma de Kőrös. I have a note to look at an article by Le Calloc'h in Tibetan Review, vol. 19 (1984) no. 11, pp. 12 17, 20. I think part or all of this has the title "Sangye Phuntsog, the Tibetan Teacher of Alexander Csoma de Koros." There's also supposed to be something about him here: Louis Ligeti, Ouvrages tibétains rédigés à l'usage de Csoma, T'oung Pao, vol. 30 (1933), pp. 26-36. Maybe it's possible to see this last one on the Persée website. I should check. That's about all I can come up with at the moment. I know Csoma did a bit on the Four Medical Tantras/Rgyud-bzhi which was based on a summary the Zangskar Lama wrote for him, and Csoma's writing of 1839 was maybe the first to generally discuss the content of the Four Medical Tantras in any language beyond Tibetan and Mongolian. I could be wrong about that.Yours, D.
Dear D, I first thought he might have been a Bhutanese, but then soon it became clear that it cannot be the case. But many thanks for the information. D.