Mate If the projector isn't told the hotspot password then it won't be able to access the connection, I think? If some router or bridge will be aggregating devices together before the hotspot, then that device will need to filter the projector.
Note that if a phone is doing cellular connection sharing via hotspot for many hours on many days you might run into heat problems and potentially then battery problems. Phones are somewhat tuned for intermittent/moderate use rather than 24x7 load as border router devices.