1. As a stand-alone word, it is pronounced /ˈfaɪloʊ/: This is the pronunciation used in the word "philology," the study of language.
2. As a prefix, it is pronounced /ˈfɪloʊ/: This is the pronunciation used in words like "philodendron," "philharmonic," and "philosophy."
The difference in pronunciation is subtle, but it's important to be aware of it to avoid mispronunciation.