On my iPhone Settings>ID>My iPad, the phone number shown is not one that I recognize. How do I change that number?

I assume the iPhone retrieves the number from the iPad, so I checked there and it has that number.

So the iPhone has, in fact, got the correct number?

Nope. Neither device has the right number. I only noticed when I went to my iPhone Settings >ID where all my devices are listed (iPhone, iPad, Apple TV, iMac). The description of my iPad has the wrong number. Since the iPhone was a gift I figured it might be a phone number from the previous owner, so I checked the iPad....thinking it would have the right number, as I've owned it from brand new.

But no, the iPad also has the same wrong number. I've sent an email to the previous owner of the iPhone, asking if they ever had that number. However, even if they did, why would it be on my iPad?

I assume, if the iPhone retrieves the information from the iPad, that is where I'd need to change the number. However, I don't know how.

iCloud syncing?

Did you have the iPhone or iPad first?

If your iPad has a cellular data plan, there will be a phone number associated with that plan.....that may be confirmed by going to your cellular provider's page to check your account info.

The iPad......probably 10 years or so.

Aha.....good thought. We had a cellular plan, years ago, but cancelled it. I'll have to dig through old records to check.

If that turns out to be the case, how do I eradicate the number?

If you don't have a cellular plan on the iPad, then why eradicate the number? It's not being used for anything. And down the road, if you want more connection options for the iPad, you have a number. However, the original cellular provider with whom the number is associated could probably help you.

The long answer is all cellular connected devices such as iPhones, iPads, Apple Watches have a unique "telephone number" assigned to them by the host telephone company. It is the number used by the telco to identify the device when it attaches to the telco's cellular network and is assigned the first time the device connects to the network and an account is established. That number is used ONLY by the telco network and cannot be dialed. As far as I know the only way a user can "change" the number is thorough Settings > General > Erase All Content and Settings although Erase All Network Settings might work but I have not tried it. That does not "change" the number it simply deletes it from the device and a new number will be assigned when the device is linked to a new account.

In any case you would want to be certain the device has been removed from your telco account beforehand. (I won't bore you with my long saga of what can happen if the number is not removed from the telco account first but it isn't fun and can be costly.)

FOOTNOTE: In the unique case of the Apple Watch its "phone number" is the equivalent of a clone of the paired iPhone number.