R' Shlomo Zalman Aurebach (quoted by Gershon Gold) permitted partaking in a siyum over the telephone in extenuating circumstances.
Although R' Shlomo Zalman (Minchas Shlomo 1:9) took a very strong view against using microphones/telephones to discharge obligations (such as Havdala or Tefilla), he apparently held that a siyum is different.
There is a dispute ...
Rabbi Herschel Schachter explains that this is only in a definite pikuach nefesh situation.
If the government or a physician has decided that an individual must
remain in isolation over the course of Yom Tov and this individual has
a psychological condition where physicians who know this patient have
determined that there is a possibility that this ...
In light of the COVID-19 (Coronavirus) pandemic, a group of Sephardi senior Orthodox rabbis have permitted Zoom [video conferencing] for use during this year's Passover Seder (and only this year's Passover Seder), providing the video conference is established prior to the holiday beginning:
English news sources:
פסק פון הגאון הגדול רבי ישראל יעקב פישער זצ"ל ראב"ד עדה החרדית
Sorry its audio, but he says when there is no other option you can be Yotzeh over the phone, and should read along if possible.