Here's the deal ... TMZ spoke to a number of escorts in the Philly area ... and many confirm their phones have been blowing up all day with would-be clients hoping to book some company.

One of those ladies ... stage name Daisy May ... tells us the debate has been a huge boom for business, likening it to the Super Bowl.

"A lot of out-of-state callers and visitors ... Some hotels were charging as high as $600-$800 per night, those clients have money to spend, and they will spend it on entertainment," she adds.

Another escort -- "Jeanie" -- says the real madness will begin when the debate concludes ... and there'll be a mad scramble by those who did not plan ahead.

Trump and Harris are set to square off at Philly's National Constitution Center ... and while the bars may be packed ... a lot of escorts won't be there to entice anyone, worker Susie Rose tells TMZ.

To be more careful, she and others have been screening clients closely, with some working out of their own homes tonight … not out of bars or other establishments … which is a safety issue.

Meanwhile, in Vegas ... William Paccione, COO of The Chicken Ranch brothel -- just outside Sin City -- said the biz will be hosting a horny watch party of their own ... showing the debate on multiple bar TVs.

Girls who are not "busy" will likely be watching the debate while a steady stream of customers visits ... and pizzas will be ordered if the joint gets really bumping, WP tells TMZ.