According to the Adobe documentation, by combining in-store purchase data with online purchase data using a phone number as the primary key, the retailer can create more accurate segments of customers based on their purchase behavior across channels. For example, the retailer can target in-store purchasers who have not bought online yet, or frequent purchasers who have bought both online and offline multiple times. These segments can be targeted in paid campaigns to increase conversion rates and reduce cost per acquisition (CPA). Reference:https://experienceleague.adobe.com/docs/experience-platform/segmentation/home.html?lang=en#segmentation