If the end of the leaf turns brown, that is winter damage. However the spotting is different. There are a couple causes:

If a leaf has brown areas with white spots, it probably has a local fungal infection of Pestalotia rhododendri. This is seldom controlled with fungicides and is best mitigated by good sanitation and avoiding excessive moisture.

Leaf spotting can also be caused by chemical injury, such as drift from cleaners, paints, or chemicals used to kill moss on roofs. Sometimes the results of such injury may not show up for weeks or months.

There are a number of leaf spots or burns caused by fungi such as Botrytis cinerea, Phyllosticta, Septoria and others. Many are secondary infections happening after mechanical damage or environmental stress, such as sunburn, drought, winter damage or windburn. They generally occur during wet weather and many times are self limiting with drier weather. Good sanitation is helpful, so remove brown and fallen leaves. Also provide good air circulation. Spraying with Benomyl or similar fungicide can be useful, but is frequently not necessary.

Here is a link that might be useful: How to grow azaleas and their problems.