Penn State Police Investigating Jason Kelce Phone-Smashing Incident

Jason Kelce's altercation with an unruly spectator at the Penn State game this weekend is on law enforcement's radar ... with officials looking into the matter.

TMZ Sports has learned ... the school's Police and Public Safety agencies are investigating the viral interaction between the Philadelphia Eagles legend and a man who referred to his brother, Travis, as a homophobic slur ... and the process is "ongoing."

Kelce was in town to catch the massive showdown between Ohio State and Penn State ... which the Buckeyes ultimately won by a final score of 20-13.

In the video ... one individual is heard directing a question to Jason, saying, "Kelce, how does it feel your brother is a f***** for dating Taylor Swift?"

Kelce lost it ... turning around, grabbing someone's phone and smashing it to the ground.

TMZ Sports obtained additional footage ... showing the person shoving Kelce, demanding he give him his phone back -- when Kelce shouted three times, "Who is the f***** now?"

ESPN declined to comment on the matter ... but it'll be revealed in a matter of hours if Kelce's TV gig has been affected by it all -- as "Monday Night Countdown" is slated to air soon.