Are six red phantoms too little?

I got eight red phantom tetras a few months ago but have since lost two (months apart from one another, the first died during acclimation, the second I'm not really sure about as all other fish in the tank seem well and parameters are stable).
The question is, do I leave them as they are or do I need two or three more?

For reference, the tank is a 33g long, heavily planted and stocked with:
eight rumminose tetras
six red phantom tetras
nine pygmy corys
six ottos
three honey gourami
and a number of neocaridina shrimp

we've never had a nitrite spike or ammonia since the establishment of the tank but I'm still cautious/scared of overstocking
I've done a lot of research but am still ultimately new to the hobby