How to differential two iphones that share the same Apple ID, apps and contacts

What do you mean by "differentiate"? Apple IDs are intended to be used by one person. Are you trying to share one? If so, there are workarounds for somethings but, as Apple changes things, they tend to break. Do yourself a favor and get everyone their own ID.

If both phones are yours, it would help if you explain exactly what it is you're trying to achieve.

Okay, so what do you mean by differentiate? What are you trying to accomplish.

Where in settings did the Apple Support person tell you to enter a phone number? What was the exact question you asked them?

Lawrence Finch wrote:

Go to Settings/General/About. You can edit the names of the phones. Just make them different. The name can be almost anything; my phone, for example is Don’t Panic, and my iPad is Ada Lovelace.

Awesome!

The last time I was in school, in the mid nineties, the college still had a computer center because not everyone had their own. They also had two network printers, Admiral Grace Hopper and Ada Lovelace.

Go to Settings/General/About. You can edit the names of the phones. Just make them different. The name can be almost anything; my phone, for example is Don’t Panic, and my iPad is Ada Lovelace.

You should not share your Apple ID with anyone.

Each person, regardless of age, needs her/his own Apple ID.