The correct spelling of the phrase is "their backs," not "there backs." The word "their" is a possessive pronoun that indicates ownership or association with a group of people. It is pronounced as /ðɛr/ in IPA phonetic transcription, with the voiced dental fricative /ð/ indicating the first two letters of the word, and the vowel sound /ɛ/ followed by the consonant /r/ representing the final letters. Proper spelling and pronunciation are important for effective communication in written and spoken English.