List<String> phones = new ArrayList<String>();
    Collections.addAll(phones, "iPhone X", "Nokia 9", "Huawei Nexus 6P",
            "Samsung Galaxy S8", "LG G6", "Xiaomi MI6", "Sony Xperia Z5",
            "ASUS Zenfone 3", "Meizu Pro 6", "Heizu Pro 6",
            "Pixel 2");

phones.stream().sorted(Comparator.comparingInt(String::length).reversed()).forEach(System.out::println);

Samsung Galaxy S8
Huawei Nexus 6P
Sony Xperia Z5
ASUS Zenfone 3
Meizu Pro 6
Heizu Pro 6
Xiaomi MI6
iPhone X
Nokia 9
Pixel 2
LG G6

Sony Xperia Z5
 ASUS Zenfone 3

Meizu Pro 6
    Heizu Pro 6