PHILADELPHIA — Comcast told employees it’s time to come back to work — in person. Starting Sept. 12, all U.S.-based Comcast cable and corporate workers will need to work three days a week in the office, according to a company memo and spokespeople. That includes the 8,000 employees who will work in the two downtown Philadelphia towers. Comcast is designating “common” days — Tuesday, Wednesday, and Thursday — for in-office work, while on Mondays and Fridays, employees can work remotely. “In-person interaction … is core to our company and culture,” said the memo, distributed nationally. “We ne…