Database index not used, when quering phrases by name

We have index on Phrase column, which is good. Phrases are loaded using this database query:

SELECT PhraseId, Translation
FROM Phrase
WHERE (LanguageId = 1) AND (UPPER(Phrase) = 'lu_SamplePhrase')

In mentioned above query phrase column value is uppercased and then compared to phrase name to be loaded. In this case, according to MySQL documentation, index is not used.