The previous exercise demonstrate how to "Query Contacts database" for all contacts, "Search for contacts with phone number only" and "Search with selection of LIKE cause". To combine both cause to search for contacts has phone number with certain constraint in DISPLAY_NAME, combine both cause with "AND".
Change:
String selection = ContactsContract.Contacts.DISPLAY_NAME + " IS NOT NULL";
to:
String constraint = "Lau";
String selection =
ContactsContract.Contacts.HAS_PHONE_NUMBER + "=1"
+ " AND "
+ ContactsContract.Contacts.DISPLAY_NAME + " LIKE '%" + constraint + "%'";