You cannot pair the Nano 33 IoT with your phone. Pairing is an optional feature in BLE and not supported by the ArduinoBLE library.
You can simply connect from an app. Try it with one of the generic BLE apps available for iOS and Android. I like BLE Scanner from bluepixel technologies on iOS. There are plenty of alternatives.
On the Arduino you can use any of the peripheral examples available in the library. e.g.,
File -> Examples -> ArduinoBLE -> Peripheral -> BatteryMonitor
You will need to install the library using the Library Manager first.