Somehow, the cellphone slipped out of her hand.

Ngoc Tran Vo, a 30-year-old beauty with a checkered past, was on a 12th-floor balcony of the Residences at Dockside in the wee small hours Friday, looking south on the Delaware River, when her phone tumbled to a patio eight floors below.

Vo, and the man whose apartment she was visiting, called security from the posh condominium and asked them to retrieve the device, said police Capt. Laurence Nodiff, of South Detectives.

"They said they could do it at a reasonable time, but it wasn't even 4 a.m.," he said. "They couldn't disrupt the sleep of anybody who was in the [fourth floor] apartment."

Vo, who worked at Club Risqué, where she went by the name "Cherry," ventured back onto the 12th-floor balcony and apparently leaned over the railing to try and spot her phone again, Nodiff said.

"And then she just tragically falls eight floors to her death," he said.

Medics pronounced Vo dead at Dockside, on Columbus Boulevard near Catharine Street, at 4:36 a.m.

There were no signs of foul play inside the condo, Nodiff said.

Mindful of the role a faulty apartment terrace railing played in the death of a New York City woman earlier this week, the captain said he checked to see if the Dockside balcony railing was secure.

"I personally shook the railing. It was solid as a rock," he said. "It appears she was looking over the edge and probably lost her balance."

Still, investigators obtained search warrants to inspect two vehicles, a Mercedes and a Hummer, that belonged to the man with whom Vo was with before her death. His name was not released.

A medical examiner is expected to perform an autopsy on Vo, of Oxford Circle, today.

"At this point, we don't see it as anything other than a tragic accident," Nodiff said. "Obviously, the investigation is ongoing."

In 2010, Vo was sentenced to five years' probation and 150 hours of community service after she pleaded guilty to attempting to extort money from a Gladwyne businessman whom she had secretly recorded having sex.

Vo worked at the time at Delilah's, on Spring Garden Street near Front.

At Club Risqué last night, the shock and heartache over the woman's tragic death were palpable. Vo would have turned 31 in two weeks, club owner Connie Innezzelli said.

"She was sweet. She was caring. She came in, did her job and never bothered anybody," Innezzelli said. "She was well-spoken and dependable. If she said she was coming to work, she came."

Innezzelli said Vo was soft-spoken and described her as a "9 o'clock girl" who worked four or five late nights a week. Vo, a graduate of Bok Technical High School in South Philadelphia, was an entertainer at the Columbus Boulevard club and usually dressed in long gowns at work.

"She would just do her job. She was very professional," club manager Ron Crudele said.

Both Crudele and Innezzelli said Vo's absence will be felt at Risqué.

"We'll miss her dearly," Innezzelli said.