getting heated TMZ.com
Update
2:40 PM PT -- TMZ has just obtained exclusive video ... showing Jason clearly saying "Who is the f***** now?" multiple times to the person's face ... this after getting shoved to the ground by the dude.
12:56 PM PT -- More video has emerged from the incident involving Jason Kelce ... with the new angle showing the person whose phone Kelce smashed demanding it back.
A scuffle ensues, broken up by people standing near Kelce ... before he appears to yell back at the man "Who is the f***** now?