Explanation
According to the ServiceNow Product Documentation on Stock Rules1, stock rules are records that define the conditions and actions for replenishing the stock of assets in a stockroom when they drop below a specified threshold1.
According to the ServiceNow GlideFast blog post on Stock Rules in ServiceNow2, when creating a stock rule that replenishes from a vendor, the primary requirement for the warehouse stockroom is that it must have an assigned manager and the manager must have a valid email address2.
The reason for this requirement is that the stock rule will generate a purchase order for the procurement of additional assets from the vendor, and the purchase order will be sent to the stockroom manager's email address for approval2.
The other options are not primary requirements for the warehouse stockroom when creating a stock rule that replenishes from a vendor. The stockroom does not need to have an assignment group, a valid mobile phone, or a valid time zone for the stock rule to work.
References:
1: ServiceNow Product Documentation: Stock Rules
2: Stock Rules in ServiceNow - GlideFast ServiceNow