Why do Sephardi Jews sit when reciting the bracha for tefillin? Especially considering that we show honor during birkot mitzvot by standing for almost every other opportunity, it seems specifically unusual. I’ve never been able to find an originating source that explained this custom of sitting (then standing for the rosh and finger wrapping) and was wondering if you knew its reason.

Shalom, Many of the Sephardim have the custom, as you wrote - to put the arm tefillin on whilst sitting down, and then to stand whilst putting on the head tefillin. Though this is not required, and when there is no place to sit, or one is unable to stand, the tefillin should be put on anyway, nonetheless it is a very widespread sephardi custom. The source for this custom is from the Zohar (at the end of Zohar Parshat Chayai Sarah page 132 and also Zohar Bamidbar page 20) which connects the hand and head tefillin to two types of prayer, sitting and standing prayers. This source connects each of the tefillin with either sitting or standing and relates that these are two spiritual concepts that are represented by our sitting or standing. This source is quoted by some of the Rishonim (early Rabbis) and can be found in the Rema in his glosses to the Shulchan Aruch (25, 11). Even though the Rema writes that the Ashkenazi custom to stand for both the hand and head tefillin blessings, the Sephardim follow this Zohar. (See Yalkut Yosef - Sha'arit Yosef 25,52). I hope this helps you to understand the source for the practice- and appreciate the richness of all the Jewish people's customs. Blessings.