Google requires that all phone numbers used in ads are verified. Google has three ways of verifying your phone numbers:

1. The phone number used must appear on the same website that is featured in your ad.
    
2. Add your Google Ads conversion tracking tag or remarketing tag to your website.
    
3. Provide proof that you own your domain by linking your Google Search Console to your Google Ads account. Alternatively, you can add your Google Ads conversion tracking code to the landing page featured in your ad if you prefer to verify ownership of your domain without using Google Search Console. Click HERE for Google's how-to's on account linking, and HERE for their article on phone number verification. (Note: After linking your Google Ads and Google Search Console accounts, it may take several hours or days for your phone numbers to appear as verified.)

Since you are using 800.com as a third-party call tracking service, the easiest way to verify 800.com phone numbers is option 2 - set up your web conversions and tag your website with your Google tag.