To save the numeric value beginning with a + symbol, you have to add a single quote character ' before it:
'+1234567890
This is not a Make issue, as it is standard Excel and Google Sheets behaviour.
Example:
Hope this helps! Let me know if there are any further questions or issues.
— @samliew
P.S.: Did you know, the concepts of about 70% of questions asked on this forum are already covered in the Make Academy. Investing some effort into it will save you lots of time and frustration using Make later!