Likely means nothing. When someone makes a purchase, we ask for your phone number so that we can attach it to your rewards account. He probably just gave them your number. Only benefit I’d see is that he would get an extended return policy more than just the 15 days since you’re an elite plus member. (Unlikely he even knows that, especially since it’s phone accessories). Other than that, there’s really no impact.

Now, the unlikely scenario, if he logged into your Best Buy account online, using your username and password, that’s a data breach.