Simplify the following text for a Grade 17 native English-speaking person.
Original: During his years in the United States , Walter worked with many famous American orchestras , including the Chicago Symphony Orchestra , the Los Angeles Philharmonic , the NBC Symphony Orchestra , the New York Philharmonic ( where he was musical adviser from 1947 to 1949 , but declined an offer to be music director ) , and the Philadelphia Orchestra .
Simplified: He worked with many famous American orchestras , including the Chicago Symphony Orchestra , the Los Angeles Philharmonic , the NBC Symphony Orchestra , the New York Philharmonic and the Philadelphia Orchestra .