As mentioned in this question, there is a fairly widespread custom to kiss the tefillin at certain times during Shacharis, among them the parts of קריאת שמע that mention tefillin.
One of these times (recorded in this answer to the above question) is "פותח את ידיך" "poseach es yadecha" "You open Your hand" in Ashrei*. While I understand that the instances in קריאת שמע where we are commanded to put on tefillin have a connection to tefillin, I don't quite understand the connection between tefillin and this phrase in Ashrei.
Where's the source for this custom (kissing tefillin by "poseach"), and why specifically "poseach"?
* While I haven't checked many siddurim, this custom is mentioned in the Artscroll siddur, by both instances of Ashrei in Shacharis.