MB 19: But etc. - In the book Shulhan Shlomo, the author has a doubt: it is possible that this is only for one who wears tfillin all day, but not for one whose practice is to wear them [only] during the recital of Sh'ma and prayer.
MB 20: "casual eating" - It appears that the quantity [of bread] which defines "casual eating" is the volume of an egg, like the law with respect to a succah in Siman 639, see there [Thus wrote the Mateh Yehuda.]