How many open businesses in the City of Phoenix have users left a long review?
open businesses refers to active = 'true'; long review refers to review_length = 'Long'
SELECT COUNT(DISTINCT T2.business_id) FROM Reviews AS T1 INNER JOIN Business AS T2 ON T1.business_id = T2.business_id WHERE T1.review_length = 'Long' AND T2.active = 'true' AND T2.city = 'Phoenix'