Q: how do I add another phone on my account?

Go to Settings>iCloud and sign in with your iCloud ID.  Note: when you share an iCloud account like this any data you sync with the account from either phone will be merge and will appear on both phones.  Also, any actions taken on one device (like adding or deleting contacts) will also be taken on the other device.  Finally, both phones will be sharing the same iCloud email account and free 5GB of storage.