New Post: How to properly write values with leading zeroes with its unknown length

If you explicitly set a numeric value as a string like that in PHPExcel, then you will get that message..... if you enter a numeric value in MS Excel itself with leading zeroes by typing it as '123 (with the leading quote) then you'll get exactly the same message about numbers written as text from MS Excel..... it's what MS Excel does

The better option is to insert the value as a number, and set a number format mask, but without knowing the specifics of what you're trying to do, the type of values you're working with and the type of masking that you need for each, then it's very difficult to advise