Q. Dear Rabbi,
I was distracted today (Rosh Chodesh Shvat), and right after kaddish before Musaf I started davening shmoneh esrei with my tfillin on.  I said the first brocha all the ways until “Elokeinu”, when I realized that I stil had my tfillin on!  I wasn’t sure whether it was better to continue davening with my tfillin on, so as to not be mafsik in the middle of shmone esrei, or to take off my tfillin at that point in time, and continue davening after my tfillin were removed.  I decided to go with the latter option, as it also had the maileh of not being porush min ha tzibur.  Was this the correct decision?
Furthermore, if the etzem reason for not wearing tfillin is because of “keser” during kedusha, would it have made more sense, mikur hadin, to finish private shmonei esrei, than take off tfilin?
Please advise!!
A. Horav Shlomo Miller’s Shlit’a opinion is that one should not be mafsik, interrupt or disrupt the amida. Halacha considers a hefsek in shemone essrei as very severe and prejudicious, as Shulcha Aruch (O.H 104: 1) rules; that even if a King greets one while davening the amida, he should not interrupt and answer.
Although, one should indeed stop, if he is committing a sinful act during the amida, such as praying in an unclean place, davening musaf during Rosh Chodesh does not qualify as such.
(See also question 2397, regarding one that realizes during shemone ezreh, that he is wearing a hat that is not his own).
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a