Question: For all the Yelp businesses that allow customers bring their own beer, what percentage of them are in "Phoenix"?
SQL: SELECT CAST(SUM(CASE WHEN T3.city LIKE 'Phoenix' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T2.business_id) AS "percentage" FROM Attributes AS T1 INNER JOIN Business_Attributes AS T2 ON T1.attribute_id = T2.attribute_id INNER JOIN Business AS T3 ON T2.business_id = T3.business_id WHERE T1.attribute_name LIKE 'BYOB' AND T2.attribute_value LIKE 'TRUE'