Earlier quoted context omitted.
English "foot" (and the equivalent Germanic words) are cognate with the Latin word "pes" (= foot), but do not descend from it. It's not a Latin root.
Not an etymologist, but I think they still have a common ancestor (proto Indo-European?). Lots of words in Latin with p have an equivalent with f in the Germanic languages: Pater - father Pes - foot Primus - first Note the English word is not necessarily the closest to the Latin one. P and f are also considered the same sound in a few word distance metrics such as Soundex for the very same reason.
"Foot" and "pes" both descend from the same Indo-European root, but the English word has no influence from the Latin one. Compare "pedestrian", which uses the Latin root directly.