DAT One Mobile will send a 4 digit code when setting up or updating a phone number.
Tap the Account button, then the phone field and the app will ask for a phone number, enter the number and the app will text the user a 4 digit code that will complete the number verification.
To verify (or update) a phone number:
Tap the Phone number field:
Enter the correct phone number:
Check your text message there should be a text from DAT with a 4 digit code, enter that code at the prompt: