To follow up the comment above to get a female phantump you need to catch one in Wispy Ruin (It's roaming around where you get dropped of by the Shuppet) then breed it with a male Cacnea, Oddish, Bellsprout, Sunkern, Cherubi or Shuppet (these are the pokemon availabe to breed it with) also note that the event on route 3 isn't available at night