I can only find 'nyctophobic' as an adjective in dictionaries, so it looks like you have to say 'He's nyctophobic'. However, I wouldn't hesitate to recommend 'He's a nyctophobe ', but again I can't find dictionary confirmation of this, although ' claustrophobe ' and ' agoraphobe ' are just fine — as are plenty of others. w=*phobe&scwo=1&scwo=0&sswo=0
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