Siman 388
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א אָבֵל אָסוּר לְהַנִּיחַ תְּפִלִין בְּיוֹם רִאשׁוֹן; וְאַחַר שֶׁהֵנֵץ הַחַמָּה בְּיוֹם שֵׁנִי, מֻתָּר לַהֲנִיחָם.
1 A mourner is forbidden to don Tefillin on the first day; and after the sun rises on the second day, he is permitted to put them on.
ב מִבָּעֵי לֵהּ לְאָבֵל לְיַתּוֹבֵי דַּעְתֵּהּ לְכַוּוֹנֵי לִבֵּהּ לַתְּפִלִין שֶׁלֹּא יַסִיחַ דַּעְתּוֹ מֵהֶם, אֲבָל בִּשְׁעַת הֶסְפֵּד וּבְכִי לֹא מַנַּח לְהוּ.
2 A mourner is required to set his mind at ease [and] to pay attention to the Tefillin [i.e.,] not to abandon his thoughts of them; but during the time of lamentation and weeping, he does not put them on.