How do I locate another iPhone in my account

If they are all sharing the same iCloud Apple ID and location services are on, power is on, and they are connect to cell data or WiFi they should show up if you turned on Find My iPhone. If they don't then one or more of the items I listed are not true.

They don't locate them by number, it uses your Apple ID and location services. You must have activated both under iCloud on each iPhone. Again, are they all sharing one Apple ID? And how many do you have?

Log into iCloud and then open the Find My app there.

How many iPhone do you have? And are they all under one Apple ID?