The pHi-Tech Mobile App communicates with the pHi-Tech devices via BLE.
BLE stands for Bluetooth Low Energy, it is a wireless technology used for exchanging data between mobile devices over short distances. BLE provides considerably reduced power consumption.

In clear and perfect conditions the communication can be within around 100 meters.
When it comes to your poultry house,  due to shielding it can be a bit less. But if you can see the devices with your eyes you can probably connect to them.