Trav expressed sincere gratitude to his "Grotesquerie" costar Niecy Nash-Betts during the most recent episode of his "New Heights" podcast with his brother, Jason ... praising the actress for remaining tight-lipped when folks hit her up for tea on his personal life.

NNB explained her phone's been ringing off the hook ever since the Ryan Murphy show aired ... with friends and interviewers trying to get some intel on not only what happens on the show -- but also all about Traylor.

She said she never caves ... telling the Kelces she always responds with a blunt, "Get off that man's business!!"

Travis was clearly thrilled with Niecy's loyalty ... making sure she knew the gesture doesn't go unnoticed.

"I appreciate you always," Travis said. "And every time someone that has a mic in front of you always asks you something like that, thank you for always showing up. You know it’s real, and you know that me and Tay are absolutely happy."