You can copy calculations, delete the last digit of a number, and entirely clear displays on the Calculator app on iPhone.
Copy, delete, or clear numbers
Copy a calculation result: Touch and hold the calculation result in the display, tap Copy, then paste the result somewhere else, such as a note or message
Delete the last digit: If you make a mistake when you enter a number, swipe left or right on the display at the top
Clear the display: Tap the Clear (C) key to delete the last entry, or tap the All Clear (AC) key to delete all entries