Parent Customer Record > Communication > Logged Activities for its Subcustomer(s) are not Displayed

Phone calls as well as other Activity records are tracked per Customer record.  A Subcustomer is treated as a separate Customer record.
In this case, when a phone call activity is logged on a Subcustomer record, the log will not display on the Parent customer record's Communication > Activities tab.

Alternate Solution:

First create a Saved Search:

1. Navigate to Lists > Search > Saved Searches > New.
2. Select Customer as the search type.
3. Specify a Search Title.
4. Check the following boxes:
    a. Public
    b. Available as Sublist view
5. On the Results tab > Columns subtab, add the following fields:
    a. Activity fields: Company
    b. Activity fields: Type
    c. Activity fields: Title
    d. Activity fields: Date Created
    e. Activity fields: Date Completed
    f. Add more fields as necessary
6. On the Available Filters tab, add  Sub of.  and Show in Filter Region = checked
7. Click Save.

After creating the Saved Search, create a sublist:

1. Navigate to Customization > Forms > Sublists. 
2. Click the Entity tab. 
3. In the Search field, select the Saved Search created earlier.
4. Specify a Label.
5. On the Tab column, select Communication. 
6. Check Customer. 
7. Click Save.

To verify solution:

1. Navigate to Lists > Relationships > Customers > View a customer record (with a subcustomer).
2. Click the Communication tab.
3. Click the Sublist tab.