Mishnah Berurah — משנה ברורה

He should only recite the blessing "...to place" - See Pri Megadim who quotes other poskim who hold that even on the hand tefillin alone one should recite both blessings. However, the Achronim agree that on the hand tefillin alone one should only recite the blessing "...to place", since, even putting that aside, many Rishonim hold that even when putting on both tefillin, one should only recite one blessing. If one put both on but did not recite the blessings, where the halacha is that one should [still] recite the blessings [after the fact] as long as he still has them on - if he recited the blessing on the head tefillin first and then afterwards on the hand tefillin, he does not go back and repeat the blessings [in the right order]. But a priori, even if he put on the hand tefillin but did not recite the blessing on it [beforehand], he should still recite it before putting on the head tefillin.