Google Business Profile (formerly GMB) Clarifies: Phone Numbers Are Not Allow in Google Posts.

Meant to avoid the risk of spam or abuse, GBP instead allows users to include a "Call Now" button. While phone numbers have not been allowed in posts in the past, Google is providing a qualitative record when it updates its guidelines. For business owners who do not want to see their Google Posts rejected (presumably, that's most all of them), it's best to adhere to these guidelines.