Hello Bekzod,
a major change in QoS implementation happened in IOS 12.4(20)T with the introduction of the HQF = Hierachical QoS Framework
HQF is described in the link below:
https://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/quality-of-service-qos/white_paper_c11-481499.html
Now, about your question we can say the following:
a service policy applied on the physical interface can process traffic even if belonging to several subinterfaces.
This does not mean that the service policy is inherited in sub-interface configuration. The point of application is still the physical interface but it is able to process packets that are indeed part of the subinterface.
Now with the new framework you may be able to apply a different policy under a subinterface.
In other words if your physical interface is missing an IP configuration and you have only 802.1Q tagged subinterfaces applying the policy at the physical interface level should process all traffic passing over all subinterfaces.
As you have written you can check with show policy map interface <physical-interface>.
If counters increment for all classes you are Okay.
Of course this means that when you configure the class-maps you need to use ACLs that specify the correct subnets for Voice for example on multiple subinterface if needed. You need to think to the aggregate of traffic from the point of view of the physical interface level.
Hope to help
Giuseppe
