The Brother HL-L2370DW is listed as a supported printer in About AirPrint - Apple Support (en-us, September 19, 2024). This means that it should work (without an additional app) if the printer and the iPhone are connected to the same network (Wi-Fi router).
Use AirPrint to print from your iPhone or iPad - Apple Support
To begin with, after checking all settings/connections, you may want to try a full power-cycle sequence:
Power off the Wi-Fi router, the printer, the iPhone, and all other devices/computers. Wait two to three minutes. Power on the router. Wait two to three minutes. Power on the printer. Wait a minute or two. Power on the iPhone and all other devices/computers.
Also, AirPrint works with wireless (Wi-Fi) or wired (Ethernet) network connections. The Brother HL-L2370DW is capable of connecting via Ethernet as well as Wi-Fi. So, if the printer is wirelessly connected to the router today, you could carry out a test with an Ethernet cable to one of the LAN ports of the router instead. This may be more stable, and avoids some of the problems related to modern dual-band routers with "smart" device discovery and automatic band selection. The iPhone and other devices/computers can still use wireless for printing (via the Wi-Fi router).