In answer to the question as to whether to keep Yom Tov sheni shel galuyot in Eilat, your response was that as the second day is only a minhag the rabbanim take the lenient view that Yom Tov sheni should not be observed. But isn’t that in reality the stricter view with regard to wearing tefillin as well as to the inyan of bal tosef?
ב"ה Shalom, It seems that the previous answer you refered to given by Rabbi Clark is based on the view of Rav Shlomo Zalman Oirbach zt"l (שו"ת מנחת שלמה תניינא (ב - ג) סימן מו) . Indeed, as you pointed out , in the above source, Rav Oirbach zt"l wrote that due to the Mitzva of Tefillin and the problem of saying Brachot Levatala, these concrete possible "aveirot " cannot be outweighed by the "minhag" of keeping the second day. Therefore, we are lenient in regard to keeping a second day in Eilat, because of the strictness of the Mitzva of Tefillin. The question was asked a short while after the establishment of the State of Israel. Rav Tokatchinsky zt"l, asked the question by means of Rav Herzog zt"l, who was then Chief Rabbi of Israel to 18 other Rabbis ,among them the Chazon Ish, and Rav Uziel zt"l, who all said to keep one day Yom tov in Eilat based upon the opinion of the Ritva (ראש השנה דף יח) The issue is discussed at length with other opinions in: שו"ת ציץ אליעזר חלק ג סימן כג,יום טוב שני כהלכתו ח"א , עמ' שה, פרק יח:ו, פסקי תשובות סימן תצה All the best