Phone numbers dropped the first digit when I exported Excel to CSV
Phone numbers missing their first digit after exporting to CSV — almost always a lost leading zero, the same digits-versus-text problem that hits zip codes. Here's how to confirm it and keep the whole number intact
Check whether it's really the leading digit
Look at a handful of the affected numbers: is it consistently the first digit that's missing, and is that digit usually a zero? If so, this is the same leading-zero-stripping mechanism that hits zip codes and account numbers, not random data loss — Excel is treating the phone number column as numeric and numbers don't carry leading zeros.
Why phone numbers are especially exposed to this
Domestic numbers in many countries start with a 0 trunk prefix, which is exactly the digit General format discards. A leading plus sign or surrounding parentheses on an international-format number can also get stripped or cause the whole value to convert to a number in unexpected ways, since Excel's numeric coercion doesn't understand phone number punctuation at all.
Also rule out scientific notation on unusually long numbers
Phone numbers are normally well under Excel's 15-significant-digit floating point limit, so this is a less common cause than the leading zero — but if a field combines a country code, area code, and extension into one long digit string beyond 15 digits, Excel can silently zero out the trailing digits once it converts the value to scientific notation, which produces a similar "digits are missing" symptom for a completely different reason.
Keeping the whole number intact
Format the phone number column as Text before typing or pasting values into it, or prefix entries with a leading apostrophe to force text storage. When re-importing a CSV that already lost the digit, use the Text Import Wizard or Data > From Text/CSV and set that column's type to Text explicitly, rather than opening the CSV file directly and letting Excel guess.