JetBlue Airways Corp. is starting service between Boston and Phoenix on Thursday, marking its 38th nonstop destination from Logan International Airport.The Boston-Phoenix service is in addition to JetBlue’s rapid summer expansion in Boston. The airline, which is based in the New York City borough of Queens, ramped up total departures by 30 percent this summer. Under its expanded schedule, JetBlue flies about 75 flights per day from Boston.JetBlue is offering introductory fares of $99 for travel on the new route booked by Saturday for travel through Oct. 30.Shares rose 6 cents to $6.05 in morning trading.