To appear on the local network, you can use the « Shortcuts » app on iOS (or Tasker or Automate on Android) to detect that your iPhone has just connected to (or left) your home Wi-Fi network.
Then, to send the information to Gladys, on iOS you can use Gladys Plus’s Open API, I made a tutorial last week:
On Android, for someone with time and skills, it is possible to send the data via MQTT if the MQTT broker is available on the internet 