The spelling of the phrase "getting horn" may seem unusual to some, but it actually makes sense when considering the pronunciation. The word "horn" is pronounced with an /ɔ/ vowel sound, which is represented in IPA phonetic transcription as /ɔː/. Meanwhile, the ending -ing is pronounced with a /ŋ/ sound, represented as /ŋ/ in IPA. Therefore, the correct spelling of the phrase is "getting horn," with an ending -n, as it accurately reflects the pronunciation.