It appears as Phone:xxx because you don’t have a primary field defined. When you don’t have a primary field SambaPOS automatically matches Caller Id data with Phone field so it won’t match other fields. For better handling this you can configure Customer Entity as something similar to this.
On this setup the primary field name for customer is Phone and we store Customer Name as a Custom Field. We also modify Display Format to display Customer Name and Phone together on tickets and other related screens.
Since you have a Primary Field Defined SambaPOS will copy CID data to primary field so it won’t append Phone: to CID data. That means it will search all fields including mobile.
If you already have customer records you’ll need to modify them to copy phone data to primary field and customer name to custom field. You can use Batch Entity Editor for this.