hello! what app should i buy to measure room temperature inside my home

While it does have internal heat sensors that measure the temperature of specific components it still does not have a thermometer for room temperatures which I believe was your question.

You could put in an Ecobee thermostat in your home then buy external sensors for each room of your house and you could read the temperature through the Ecobee app.

For this you may need an external temperature sensor on your iPhone.

As far my knowledge and experience goes iPhones do not have external temperature sensors.

But, it has internal temperature sensors may be more than one. iOS uses these sensors to gauge when it’s necessary to shut the phone down in order to protect its circuitry from damage due to overheating. If you ever leave an iPhone sitting in the hot sun, particularly if it’s on a dark surface, you are likely to receive a Temperature Warning and if you ignore it the iPhone shuts down automatically.

The iPhone doesn't have a thermometer so there is no such app.