Whenever you enter a number, Spreadsheet assumes that it is a value and that you might want to use it in a calculation.
If you enter a number that is obviously not meant to be used in calculations, such as a phone number like 6684123, Spreadsheet can't automatically tell that it is supposed to be text. So, to enter numbers like phone or invoice numbers, you need to tell Spreadsheet not to calculate them.
To do this, type a single quote (‘) before you enter the actual number. This is necessary if you want a formula expression, such as =26 - 11, to appear as text rather than returning the result of a calculation. In this case, type '=26 - 11.
The single quote doesn’t show up in the spreadsheet. It simply indicates that the number should be treated as text rather than as a value.