What should someone do, who has the urge to use the bathroom right after saying the brachah on putting on the tefillin? Shall he put the tefillin shel yad and tefillin shel rosh and remove them? Or can he just remove the tefillin shel yad?
Put shel yad, remove it, and then go to the bathroom(Shulchan Aruch 43:1). When you return, say the bracha again(shu"t Ginat Vradim OC 1:52 and Matteh Yosef 2:11, Chayei Adam 13:66, Radvaz 6:301, Shulchan Aruch Harav 30, Maharsham 3:220, Be’er Heitev 53:3, Kitzur Shulchan Aruch 10:15, Shevet Halevi 9:3 and others).
Or, you could put shel yad on and cover it with your shirt before entering the bathroom for urination(Berachot 23a for source and shu"t Beit Ya'akov 72 allowing urinating with tefillin shel yad), but not for sitting. Our bathrooms have the din of a persian bathroom to allow this leniency b'sha'at ha'dchak based on the ruling of the poskim below and the Beit Ya'akov in accordance with the Gemara; in my opinion(see Har Tzvi O.C. 1:50, Chazon Ish O.C. 17:4, Igros Moshe E.H. 1:114, Yabia Omer 3:2, Teshuvos V’hanhagot 1:4, Be’er Moshe 4:3:9, Rivevot Ephraim 7: