A minhag in my shul is that when one of the members is having a yartzeit, he brings a cake and an alcoholic drink for the mispalelim to say a l’chaim after the davening. My question to you is if it is permitted to have a sip (and I mean no more than a sip) of the alcoholic drink with the tefillin still on.
It is prohibited to eat a meal with tefillin, for fear that one will drink at the meal, and treat the tefillin without due respect.
This prohibition refers to a meal, and not to eating outside the framework of a meal. It is also prohibited for somebody drunk to wear tefillin, but although he may not pray, we find no prohibition for somebody who has drunk a revi’is of wine to put on tefillin.
Therefore, it is permitted to have a sip of an alcoholic drink with tefillin on.
Note, however, that some rule that those who do not wear tefillin all day should not eat or drink at all with tefillin on. The common custom is to be lenient.
Sources: See Shuluchan Aruch and Mishnah Berurah, end of Siman 40 (Mishnah Berurah mentions those who rule that the permission to eat with tefillin is limited to those who wear tefillin all day). See Shulchan Shlomo (37:4) concerning somebody who is drunk (see also Sukkah 25b and rishonim, which might be the source for a prohibition on somebody drunk to wear tefillin).
There would seem to be no source prohibiting wearing tefillin after drinking even a significant amount, provided that one knows one’s ability to treat the tefillin with due respect.