Genizah of tefillin: why strict genizah for the head, but standard genizah for the arm?

Question

On the website torah.org an overview is given of ritual objects that, in case of their disposal, require a strict genizah (buried in a cemetery and sealed in earthenware or hard plastic, preferably with or near a Torah scholar) or standard genizah (buried any place that will be undisturbed).

For the bayith shel rosh (even without parashiyos) the strict genizah is considered necessary, whereas for the bayith shel yad (without parashiyos) a standard burial is deemed sufficient.

The source referenced on the website is Ginzei ha-Kodesh 6:6. I can't seem to find the source and my question is: why is the bayith shel rosh itself (the case of the head-tefillin, even without a scroll inside) considered more holy for the purposes of genizah than the bayith shel yad (the case of the arm-tefillin)?

Answer 1

The source of Ginzei Hakodesh 6:6 can be accessed here

He appears to be saying that the bayis of the shel yad (the arm tefillin) does not need to be put in an earthenware vessel and then buried, but the bayis of the shel rosh (head tefillin) does need to first be put in an earthenware vessel.

Following a bit of research and looking at the footnotes there, this can be explained as follows...

When looking at Shulchan Aruch, Orach Chaim 42 it writes:

...וקלף המעובד לשם תפילין אסור לכתוב עליו דברי חול דהזמנה כי האי גוונא לגוף הקדושה מלתא היא

[Regarding] parchment that was processed for the sake of [the mitzvah of] תפילין... it is forbidden to write mundane things on them because designation [done] in such a way [where it involves] the sacred item itself is [considered] significant (Sefaria translation)

The footnotes in Ginzei Hakodesh there notes that even though according to the Biur Halocho (42 s.v. 'guf hakedusha'), the bayis of the shel yad is considered a 'guf hakedusha' i.e. significant/holy in its own right, nevertheless, according to Rav Elyashiv zt"l and Rav Nissim Karelitz zt"l, since it lacks the raised 'shin' on it like the bayis of the shel rosh it does not need to be put in an earthenware vessel before being buried.