This is typically due to duplicate phone numbers in the CSV. Because we ignore duplicate contacts in the CSV, you may see a difference between the number of contacts in your CSV and the Progress column.
For example, If you upload a CSV with 100 contacts, 10 of which are duplicates, the upload will succeed, but only the 90 unique phone numbers will be dialed, and the status could display "5/90" in the Progress column, which means five dialed (so far) out of 90.