It’s possible to create a kind of bridge via lora between any compatible devices and lora registered gateway? Or is mandatory for devices to connect directly to a server over MQTT?
Basically, I want to view in real time some data values on my phone or other lora compatible device, data recevied from an ttn registered gateway.
LoRaWan (vs other uses of LoRa) devices connect through one or more gateways to a server, for example a private instance of LoRa Server which what this site is about, or TTN which is a collection of shared servers supporting a pool of community gateways that is not really on topic here - there is some friendly interchange of information but they have their own forum, and if you are using TTN then you are not using LoRa Server, but rather the TTN servers.
Your phone is probably not LoRa compatible, and so also not LoRaWan compatible. Instead it would interchange data with a LoRa Server (or TTN’s servers) via an Internet mechanism like MQTT.
So in effect, you could have a communication flow of
Device -> LoRaWan -> Gateway -> Server -> Internet(MQTT) -> phone
and to a more limited degree responses in the reverse direction.
That’s leaving out a lot of implementation detail (for example MQTT may also be used between the gateways and the server) but hopefully gives you an idea of the overall situation and if this is, or more likely is not, the appropriate place for your question.