how to use land line as phone number on Apple ID

You cannot use a landline as a primary 2FA device, but you can use it as an additional trusted number. And when you use a Mac or an iPhone you aren’t using the phone number, the code goes as a notification to the device, not the number.

What it is telling you is to verify the choice of a landline as a trusted number using your Mac or iPhone. If it didn’t do that any stranger could register their landline, thus defeating 2FA.

EricR3D wrote:

So, it seems that my cell, which is Android, is just a trusted number. Not what verification codes get sent to. Just logging back into the forum, I saw that. The verification got sent to my iPad (and presumably Mac too).

What is a trusted number used for?

Yes, verification codes will be sent to the trusted number. I used it once when I mislaid my iPhone and needed to log into iCloud from a work computer. The system made a voice call to the trusted number and spoke the verification code.

Landlines are not easy to receive verification codes so I would not use that as your primary trusted phone number

You might have to use a email to get verification codes, if that option is available.

A trusted number is used when you don’t have a trusted device available. When the prompt for the authentication code appears click or tap “did not get code” and a list of your trusted numbers will appear. Chose one to have a code sent to it.

AlWeir wrote:

You might have to use a email to get verification codes, if that option is available.

To the best of my knowledge, email is not an option with Apple’s 2FA.