I second 1077. At least six of any tetra species will mean less stressed [= healthier] fish.
When you say "school with" it could mean two different things. First, most tetra will not "school" with other species, except now and then; the species that are schooling (or more correctly shoaling) tend to remain together. But the second meaning could be compatibility, and any non-aggressive tetra will be compatible with Pristella.
However, here you should research the fish thoroughly. Pristella are more active than some, and do like a bit more water movement. Black phantoms are quite the opposite. If the tank is spacious, say 3-feet long or more, this can work as the Pristella will remain closer to the filter outflow and the Phantom at the opposite end. Look for active swimming tetra species. Or perhaps small danio, those there is not a lot of different colour in the danio. Neon tetra would do well with Pristella.