- Implement upsert logic in import_phone() function
- Check for existing (id, phone) combinations before insert
- Track duplicates within CSV to skip gracefully
- Update existing records instead of failing on duplicates
- Add detailed statistics: inserted, updated, skipped counts
- Align with upsert pattern used in other import functions
- Add documentation in docs/PHONE_IMPORT_FIX.md
Fixes: UNIQUE constraint failed: phone.id, phone.phone error
when re-importing or uploading CSV with duplicate entries
