If you want to use the Phone call option, please make sure you don't have any redirection or automatic voicemail set up, in that case you won't be able to proceed.
Before integrating the number you need to do the Facebook Business Verification:
In the past we were not able to integrate VOIP numbers successfully. However phone numbers provided from Twilio worked well. You also have the option to choose a phone number provided from Meta during the WhatsApp Integration process. However this will be an US number.