Sam: That’s circular logic. The reason a woman cant wear a tallis is because of beged ish. but its only beged ish if women were banned from wearing talleisim- but they’re not! regarding tefillin, chazal say michal wore it. many hold rashi’s daughters did too.
rambams rule about mitzvos shehazman geramah should hold up for women wearing tefillin. if you disagree with that, its on you to bring a rayah. just know its a big deal to go against a pashut rambam.