How can I convert Map<String, String> to Map<String, List<String>>?

[Max_26]

I have the following Java code snippet:

        Map<String, List<String>> phones = new HashMap<>();
        phones.put("User1", Arrays.asList("0502324547", "0651634767"));
        phones.put("User2", Arrays.asList("0977634321", "0697654221"));
        phones.put("User3", Collections.singletonList("0970011223"));

        Map<String, String> map = phones
                .entrySet()
                .stream()
                .flatMap(e -> e.getValue().stream().map(v -> new AbstractMap.SimpleEntry<>(v, e.getKey())))
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));

Using it I'm converting

Map<String, List <String>>

to

Map<String, String>

and then passing to the method like:

public Map<String, List<String>> createNotebook(Map<String, String> phones) {
        Map<String, List<String>> collectionsMap = new HashMap<>();
         // here I want to convert vice versa

        return collectionsMap;
    }

Can I do similar to this, but vice versa?