Check out the video ... you see the Chiefs tight end being filmed by a fellow concertgoer at the Singapore show he went to this week -- and while Taylor was belting out "I Knew You Were Trouble" ... TK was checking his phone, right at the peak of the song.

The person who filmed this seemed to be throwing some shade Travis's way -- by suggesting he wasn't being attentive enough .... with a caption, reading "It's giving supporting bf."

Despite what the TikToker might've been trying to imply here -- T-Swift's legion wasn't biting ... with a ton of people jumping to speak up for Travis ... and rightly pointing out how ridiculous any type of scrutiny or criticism over this really is. Dude's just checking his phone!

A few Swifties even noted that this is the first time that Travis has ever been seen looking at his phone while cheering on his sweetheart.

Besides, we know Travis is a supportive boyfriend -- evidenced by the fact that he's literally there in Singapore right now. As we reported earlier today, Trav was having a great time at the concert -- he was even caught dancing his tail off to Taylor's jams.

There's no denying he's a true fan of the Grammy winner ... remember, Travis attended the "Eras" tour before he and the pop star even got together. And, since getting with her -- he's made a huge effort to be at some of her international tours ... including in Australia.

Clearly, he's a supportive significant other ... and it seems her fans know that quite well. Here's hoping Trav can shake off the shade ... because it really ain't all that deep.

The guy's allowed to look away for a moment, y'all ... it should go without saying.