The correct way to use
TEXT is to apply it as a function, not as a switch to the concatenate function. However, in most cases you would want the referring cell to hold the number in proper numeric form, not a textual representation of the number.
So, most likely you need the formula
=A1 in cell B1. You then select menu item
Numbers. Pick a suitable form from the list.
If you really need the number in textual form (e.g. for more reliable extraction/manipulation of individual digits), use the formula
This makes the content of B1 unreliable for use in further calculations.