For context, Papyrus just found out earlier that his brother Sans attempted suicide, and supposedly failed. He finds him alone at a grill and bar later that day.
I’m not great with dialogue, but I hope I did okay!
"Sans!" a familiar voice breathlessly called out, bursting through the door of the pub. Just his luck.
Locating Sans amidst the empty tables, he sped his way to the opposite side of the booth with the brightest smile Sans might've ever seen on Papyrus. It suited him well, to tell the truth.
"Sans—I nearly forgot to tell you!" Papyrus gasped out. He didn't wait at all to regain his breath before speaking again. Sans figured it was just another learned behavior from being around dogs so often. "I was going to train with Undyne today, but I saw you left your phone at home, so I'm thinking, hey! I should go return it to you, right?"
"But then I thought of all the things you said to me earlier, and how I should've done more for you… and then it hit me! This could be the perfect chance to tell you how much you mean to me! I can't have you doubting our brotherly friendship ever again."
"Oh." Sans paused. "That… actually means a lot to me, Papyrus. Thanks."
"You said you had my phone?"
Papyrus opened his mouth to reply, but hesitation assumed control.