The correctional officer presses a button on his phone to signal Batman, and the phone on the screen turns red as it dials The Caped Crusader.
Though we cannot officially confirm that it is a nod to Batman ’66, the general understanding of the Reddit user who posted the image seems to be that it’s a nod to the same red phone used by Adam West’s Batman back during the character’s campy days on the small screen.
That shot is of the phone used by Bruce Wayne’s informant at Iron Heights prison when Barry Allen goes to visit his wrongfully-incarcerated father.
It’s an incredibly quick moment, but easy to understand once the average Bat-fan actually finds it.