Huh, never looked into that reference myself! "E.P.H.E." does seem to stand for "Ecole Pratique des Hautes Etudes," an organization that has a website for their publications (
https://www.ephe.psl.eu/ressources-savoirs/publications-de-lephe-psl), but of all the ones listed, I presume it's "Les Conférences" that might contain an Ellenberger paper, if it exists. However, their conference volumes online only go back to 2010. However, poking around on Worldcat, there appears to be a 1972–73 conference volume for the organization (
https://search.worldcat.org/title/1124730432)...but according to Worldcat, only a single library in France has the volume. Brief poking around on Gallica didn't find it, though Gallica's search function leaves some things to be desired (or else my understanding of how to search it effectively leaves some things to be desired!). That's as far as my sleuthing brought me. I'd love to at least see a table of contents for the volume if not the volume itself!