While she made no specific threat against schools, Mr Phillips said her comments made her a danger.
Police are searching for an 18-year-old woman, Sol Pais, who investigators believe traveled to Colorado from Miami on Monday night and "made threats to the Denver metropolitan area", the Jefferson County Sheriff's office said on Facebook Tuesday.
A "BOLO" sent out by Rocky Mountain Safe Streets Task Force says that Pais is "infatuated with Columbine school shooting" and was "attempting to buy firearms".
Another neighbor, who did not want to be identified, said her children attended Miami Beach High School with Pais. Authorities requested the lockout in Jefferson County on Tuesday afternoon as they searched for the suspect, whose description was released on Twitter with a warning not to approach her.
The sheriff's Twitter post, which included two photos of Pais, said she was dressed in a black T-shirt, camouflage trousers and black boots.
"It's a credible threat ... but she did not make it directly", said Jenny Fulton, a spokeswoman with the sheriff's office.
Authorities say tightened security at Columbine High School and about a dozen other Denver-area schools is related to an FBI investigation.
On Tuesday, the Jefferson County Sheriff's Office placed Columbine and 21 surrounding schools under a security "lockout", allowing activities inside to continue as usual but restricting entry and exit at the schools.
Two hours after announcing the lockouts, the school system reported that all students and staff were safe, adding that students would be released from the schools and buses would run on their normal schedule, though some may be slightly delayed.
Jenny Fulton, another sheriff's spokesperson, said the FBI was investigating the apparent threat.
Teenage gunmen attacked Columbine on April 20, 1999, killing 12 classmates and a teacher. Columbine High School is in Jefferson County.
Please call the Federal Bureau of Investigation tipline at (303) 630-6227 where your call will be answered immediately if you have seen this individual or have information on her whereabouts.
"And in that regard, I know that this opens a wound, especially on this anniversary week, for those families who were most deeply impacted by this", Jefferson County Sheriff Jeff Shrader said. There was no immediate indication whether there was any connection to the anniversary.
The undisclosed threats led Columbine and several other high schools outside Denver to lock their doors for almost three hours. Extra precautions were taken at schools near Columbine, where sheriff's deputies were on hand.
Islanders Silence Mighty Pens Again, Take 3-0 Series Lead
At home in front of a boisterous crowd should create positive vibes for a Pittsburgh squad searching for any sort of magic. The Islanders went 0 for 2 on the power play, squandering a 30-second two-man advantage in the second period.
'Today' show co-host adopts another daughter
In March, Hoda couldn't help but gush over her boyfriend of six years. "It felt nearly selfish", Kotb explained . Kotb and TODAY also revealed that the newest addition to the family's name is Hope Catherine Kotb .
Qualcomm and Apple drop lawsuits against each other
Qualcomm stock rose more than 20% after the news broke, boosting its market cap by about $14.5 billion to more than $84 billion. The trial ballooned into a $27 billion, five-week affair with Qualcomm wanting damages of its own for breach of contract.
Bernie Sanders defends Ilhan Omar: She's not antisemitic
But, she added: "It's absolutely abhorrent the comments she continues to make and has made and (Democrats) look the other way". Sanders defended Omar's remarks by attacking Trump in a tweet, writing: " Ilhan Omar is a leader with strength and courage".
Falcon Heavy center core toppled after landing
SpaceX didn't provide any information on the status of the booster core, including whether it will be retrieved at all. The mission from pad 39A marked the first time all boosters from a Falcon Heavy rocket were recovered successfully.
Aretha Franklin honored with posthumous Pulitzer
The Capital Gazette was given a special citation for its coverage and courage in the face of a massacre in its own newsroom. Aretha Franklin is now the first individual woman to receive a special citation prize, which was first awarded in 1930.