Iphone12 calculator does not show formula

If you mean the calculator doesn't show what you've already typed, no, it doesn't.

You might want to look at a third-party calculator app. I have one on my phone called Calzy that's attractive and shows what you've entered so far. It even has a History button that shows past calculations. I have no idea what it might have cost. And, there are certainly lots of calculator apps that do this sort of thing.

Ah, yes, now I understand, thanks. That is something Apple’s Calculator app never did. However, it can always be done using Spotlight!

Use Search on your iPhone, iPad, or iPod touch - Apple Support

Best I can tell, it's $2.99 which doesn't seem a lot to pay if those features are important to you. It has lots of other options like calculating taxes and making adjustments in the text size and color.

Rotate the iPhone to landscape mode.

Calzy shows this:

I think the OP is looking for the numbers and operators (I don't think "formula" is the right word) that show under the answer.

As IdrisSeabright suggests, perhaps I don’t understand what you’re expecting to see.

This is what you would see in the Calculator app.

Oh, I forgot you could do that with Spotlight! Cool. Might save the OP some money.

I should have explained Spotlight and iPhone Search are the same thing.