The spelling of the word "SSPSPI" can be explained through the use of IPA phonetic transcription. The word is comprised of six individual sounds, including the voiceless alveolar fricative "s," the voiceless bilabial plosive "p," and the voiceless postalveolar fricative "sh." These sounds are repeated twice, followed by the voiceless bilabial plosive "p" and the voiceless alveolar plosive "t." The unique combination of these six sounds forms the word "SSPSPI," which can be pronounced by following the IPA transcription.