Fix Excel E+11 Number Format
Open the CSV file in Microsoft Excel. When the Text Import Wizard appears, tick "Comma" as the delimiter and click "Next".

Select the column showing E+11 numbers. Right-click and choose "Format Cells".

In Format Cells, select the Number category with 0 decimal places as shown. Click OK.

The phone numbers will now display correctly. Save the file as CSV again before uploading to iSMS.