We knew the Phalcon is very faster than other framework .
check this https://docs.phalcon.io/en/latest/reference/benchmark/hello-world.html
But does Phalcon still need Memcache to improve speed ?
Access a busy database is expensive for a web application, it often involves many accesses to hard disks and/or networks , Memcached allows you to temporary store data directly in memory instead of access a busy database all the time improving speed.
You can get rid of default session's handler (files) and to use memcacheD as a session bag instead. So, it is favorable to cache some apps parts even with Phalcon.