/n/ assimilates to /p/ and is realized as /m/.
/ë/ is raised to /u/ in anticipation of /w/.
/wà/ is realized as /ò/ but is raised to /u/ under influence of preceding /u/.
Note: the underlying form could also be posited as /n-pèshëw-ëk-w-àk/ with /-ëwë/ realized as /u/, a contraction that has probably contributed to reanalysis of the base as /pèsh/ for some speakers.