Based on this Avengers Headcanon:

"Phil has a collection of mint condition Iron Man cards as well as Captain America ones. He keeps these under lock and key, because he'd already gotten them signed by a righteously smug Tony, and doesn't let anyone else see them."

Not so much the 'righteously smug' part, but the same basic premise.

Tony had found them accidentally. No one was supposed to know they existed, let alone Tony himself, but with how often the billionaire intruded on his personal space, and how he wanted to investigate every shiny new thing he touched, Phil was - quite frankly - a bit surprised it had taken him that long to find them. Not that Phil hadn't put up security measures to make sure they weren't found, but it was Tony Stark they were talking about. He hacked into the Helicarrier's personal databases when he was bored.

So yeah, Phil had (futilely) attempted to keep the cards a secret from the man in question, even though he damn well knew at the back of his mind that it would only be a matter of time before Tony discovered them. It started with the genius letting himself into Phil's more-security-measures-than-strictly-protocol apartment (some of which had been created and installed by said genius, which was good for keeping out potential burglars and assassins, but did absolutely nothing in keeping out Tony himself). Phil had been in the process of packing up his meager belongings to move into the Tower with the rest of the team (because as their personal babysitter, he had to make sure they didn't kill each other every time movie night rolled around and they got into another fight-to-the-death for who held the popcorn bowl), so Tony's visit had come as something of a pleasant surprise. He could certainly use the help, and if Tony refused, he could tase him. It was a win-win.

Tony had come in whining about how Steve and Natasha had teamed up to whoop his ass in the gym, and Clint had laughed at him when he was slammed into the mat (which happened one time too many, according to Tony). Phil had silently agreed with him; most of his skin was an unhealthy shade of purple, and when he had removed his sunglasses Phil had immediately noticed the intimidating black eye he sported. He had sighed and sat him down on the sunken leather couch he had yet to donate somewhere while he went to grab the first-aid kit from the cramped bathroom next to the kitchen nook.

It was not his fault he'd forgotten that Tony was handsy when left to his own devices, especially in a new place with everything packed into untaped boxes in plain view.

It was also not his fault that his vintage card collection just so happened to have been set on the coffee table when Tony had so brazenly announced his presence.

And so, when Phil had returned to the living area, it was to find Tony examining a handful of cards, an unidentifiable look on his face. Phil guessed from the color of the cards that he'd dug through the box until he'd found the Iron Man ones. Phil could only bring himself to sigh, which had attracted Tony's attention, and made him look up from the cards curiously.

When he'd seen Phil, he had grinned and jumped to his feet, excitement rolling off of him in waves. Phil had simply raised an eyebrow at his behavior, at least until Tony had stepped in front of him after leaping from his seat on the sofa, nearly buzzing with energy, and held out the cards to ask, "Can I sign them?"

Phil had blinked.

Tony's grin hadn't diminished, and he had to ask again to get a proper answer out of the stunned agent. Phil had shaken himself lightly to clear his head, before giving the cards a look, and then casting that very same look on Tony, who still looked immeasurably happy, as though his entire week had just been made ten-thousand times better. It was the happiest he'd ever seen the man, actually, so he couldn't be blamed for nodding his agreement.

If Tony had let out a squeak of what could only be described as glee after the fact, Phil didn't mention it. He didn't mention how Tony had nearly stumbled in his haste to get the kitchen nook to find a pen, either.