Mishnah Berurah — משנה ברורה

The three Kedushot - This is a publishers error, and in truth it should say "the three Kaddishim and four Kedushot" - because "Barchu et Hashem" is considered the first, since it's an expression of sanctity, the Kedusha of "Safa berurah" is the second, [then comes] the Kedusha in the Amidah, and then the Kedusha of "Uva Letzion". The three Kaddishim are the Half Kaddish recited before Barchu, the Half Kaddish after Shemoneh Esrei, and the Full Kaddish after "Uva Letzion". Nevertheless, it seems from the Pre Megadim and other Achronim that in places where the custom is to recite Kaddish Yatom every day after Aleinu, it's better to not remove one's tefillin until after the Kaddish Yatom. Those who fold their tallit and [wind up] their tefillin and put them away in their pouch while Kaddish Yatom is being said are not acting properly, for one should have utmost concentration while answering "Amen Yehei Sh'mei Rabba", as is explained below in siman 56 in the Tur and Shulchan Aruch. "Amen Yehei Sh'mei Rabba" is on an ever higher level than Kedusha as is explained there in Magen Avraham se'if katan 1. And it's certainly not any worse than all other rabbinic level blessings which one is forbidden from doing anything insignificant while reciting the blessing, as is explained below in siman 191 in Magen Avraham se'if katan 2.