PL/SQL (Procedural Language/Structured Query Language) in Phalcon

Yes, plsql methods can be called from model.

  $set = $database->query("SELECT method_name_here(?,?,?)", array($json, $id, $uuid));
  $set->setFetchMode(Db::FETCH_ASSOC);
  $result = $set->fetch(); 

I'm using postgres

Yes, there is an extensive documentation available here: https://docs.phalcon.io/en/latest/reference/phql.html