How do I recover my missing Contacts on my iPhone 16 Plus?

The contacts that are displayed in the Contacts app are actually a collection of contacts from one or more sources that can be stored on your iPhone as well as in online accounts such as iCloud, Gmail, Microsoft, Yahoo, etc. When some of your contacts disappear, it is caused by either having toggled off the use of Contacts from a given account, or that the entire account is unavailable on the iPhone.

You can see the sources of contacts on your iPhone in: Settings > Apps > Contacts > Contacts Accounts

That dialog shows you which accounts that are configured on your iPhone. Tap on one of those accounts and you can see if "Contacts" are enabled for that particular account. If you know which of your accounts contained the contacts that have disappeared, first make sure that Contacts are enabled on that page. If they are but the contacts are still gone, then go to the Mail app and try to send and receive a test email to yourself. Doing so is a way to test that your login is valid for the service and that you have a network connection available. If prompted for your password at that point, then entering it may reestablish a connection to the service and allow your contacts to appear again.

I would suggest literally laying the iPad and iPhone next to each other and opening the Contacts app on each. In the upper left, touch "< Lists". Then compare these sources of contacts on each. Do they match exactly on both devices? There is also a count next to each account that shows how many contacts are stored in each account. If your iPad and iPhone do not display the same information here, then you have discovered where your missing contacts are. Let us know and someone can help you get those contacts to show up.

While you are at it, check on your iPad for the account displayed at Settings > Apps > Contacts > Default Account. That setting may not be present if you only have one account that provide Contacts. But if that setting is listed, it determines where new contacts are stored when created. Make sure that your iPhone and iPad are both using the same default account so new contacts you create show up on both devices.

What I forgot to tell you is to pay attention on the contact "Lists" dialog and let us know if you have "iPhone" listed as an account section. If you have that listed on the iPad, but not the iPhone, then I am guessing that your missing contacts are stored locally only on the iPad device itself.