Could you imagine getting on an airplane ... WITHOUT YOUR PHONE?!
Nightmare, right?!
Well, that's ALMOST what happened to "This Is Us" star Sterling K. Brown ... if not for the heroic actions of Lakers rookie Josh Hart!
Brown tells us he left his phone in the car and ALMOST had to suffer an entire flight without Twitter, Instagram and all the movies and TV shows he had on his cell.
Well, thankfully for him ... Hart was there to save the day!
We caught the whole thing on video -- and afterward, Hart told us he wants to treat Brown as his guest to a Lakers game next season!
Pretty cool, right?