You have two options to add contacts. You can either use HubSpot CRM or Aardvark's contact manager.
With HubSpot, you can connect to Aardvark via an integration. Once connected, any contact you add will automatically associate with Aardvark when you schedule a meeting with that contact. Aardvark will use the email from your calendar invite to find the contact in HubSpot and HubSpot will look at the phone number you have added to tell us what phone number to send the SMS to. Learn more about creating contacts in HubSpot here.
Aardvark contact manager
The Aardvark contact manager allows you to manage emails, names, and phone numbers of contacts in your database. This is a simple way of ensuring that your email calendar invites can link up to a phone number. You can add contacts manually through the add contact button or upload a CSV of users. The CSV must contain exactly company, first, last, email, phone columns.