DB::select($query) returns an array of stdclass objects, not a collection. However, it is possible to convert it using the collect() function:
$pbs = DB::select('EXECUTE [dbo].[spQueryContainer]');
$pbCollection = collect($pbs); //Transform the array into a Laravel Collection of stdclass
return PBResource::collection($pbCollection);
Even if the Collection contains the wrong Type (stdclass instead of PB), the resource will still use it as long as the given objects have all the attributes used in your resource.
If you want a cleaner solution, you should try to convert the stdclass object to a PB object. The topic is discussed on this post.