To find your wife's phone using the Find My app on your iPhone, you can follow these steps:

Open the Find My app on your iPhone.

If you're signed in with your own Apple ID, tap the "Me" tab at the bottom of the screen and switch to your wife's Apple ID by tapping the icon in the top left corner of the screen and selecting her name.

If you're not signed in with your wife's Apple ID, tap the "People" tab at the bottom of the screen and select your wife's name from the list of contacts.

If your wife's phone is currently online and connected to a cellular or Wi-Fi network, you should see its current location on the map in the app. You can zoom in and out on the map to see the location more clearly, and tap on the location to get more details like the battery level and driving directions.

If your wife's phone is not currently online, you may still be able to see its last known location on the map. This can be helpful in determining where it was last seen and potentially locating it if it's lost or stolen.

If you need to take additional actions like playing a sound on the phone to help locate it or remotely locking or erasing it for security reasons, you can do so using the options in the Find My app.

Note that in order to use the Find My app to locate your wife's phone, she must have enabled the Find My feature on her phone and allowed you to see her location. If she hasn't done so, you may not be able to locate her phone using the Find My app.