Crushed, they posted a note about the encounter on Facebook and soon the cake had become a cause, with the sides becoming stand-ins for the culture wars: Phillips was portrayed as the intolerant business owner. The couple became the gay rights activists pushing their agenda, some claimed.
It was one of several incidents that inspired legislation in at least 11 states that would have allowed business owners to cite their religious beliefs in denying service to patrons. Most have died amid a national outcry that they would legalize discrimination.
Along the way, the stories of those caught up in the clash over fast-changing social mores can get lost. Phillips, Craig and Mullins are just three.
Phillips, 57, grew up near the teeming strip mall that houses his bakery in Lakewood, on the edge of Denver's suburban sprawl.
After graduating high school, Phillips went to work at a bakery and found he enjoyed the adrenaline kick and sense of achievement that came from catching doughnuts as they came off the conveyor belt and glazing and sprinkling them.
Nowadays, he loves his work for the way it lets him improve people's lives. "That's," he said, "what Christ does."
Phillips grew up in a religious household, but in his early 20s he felt adrift. He drank and fathered two children with his girlfriend Debbie. As he was driving one day, he felt something extraordinary. "The Holy Spirit convicted me of my sin," he recalled.
Shaken, he told Debbie that night he had found Christ. She said the same had just happened to her. They married and had a third child.
Eventually Phillips started his own shop, serving residents of the new housing developments that were rising nearby. His daughter and 87-year-old mother also work there now.
From the start, he knew there'd be limitations on what he could do. "In everything I do, I think about how people will perceive Christ through me, by what I sell, what I make," Phillips said.
The display cases bulge with cakes of every color. One depicted a trio of crosses on a hill, with the words "He Has Risen."
Phillips takes his cake-making personally. As he prepares a cake for a child's first birthday, Phillips makes a separate cupcake-sized piece to be placed on the kid's high chair, envisioning the moment the tot will dig into it, smearing frosting across his or her face.
For weddings, he interviews the couple to find out how they met, their mutual interests, what color dresses the bridesmaids will wear.