Philip lost his leg in a bizarre Iraq mission in 2004 or 2005, which involved Sami as Dan, if I recall correctly.
He's some of that history:
Philip and Belle got engaged, with Philip thrilled that he and Belle were going to be able to live their lives together. Unfortunately, just as they were getting engaged, Philip was being called to active duty in Iraq. The two moved up their wedding plans, getting married immediately before Philip had to ship out. Philip returned home, but he had lost the lower part of his leg in connection to a Tony DiMera plot. He was thrilled to learn of Belle's pregnancy. Claire Kiriakis was born at St. Luke's on what was supposed to have been her maternal half-aunt Sami's wedding to her paternal half-uncle Lucas. Unfortunately, the wedding never happened.
Philip, Belle and the baby were transported to the hospital, and it was there that Belle and Philip chose their daughter's name -- it was a mutual favorite -- and Shawn and Mimi consented to be the child's godparents. When baby Claire became ill, Kate learned that her blood type was AB- and after talking to a medical student realized that there was no way Philip could be Claire's father, and soon realized that it must be Shawn. Unfortunately for poor Claire, her health continued to deteriorate, and it wasn't long before Lexie Carver realized that if Claire didn't get a liver transplant, she wouldn't survive. Luckily for Claire, Zack Brady was a match, and she received his liver after he died.
Claire recovered, and her parents were thrilled, but when the truth finally emerged about her paternity, thanks to Chelsea's intervention, Philip left town for a number of weeks, and Shawn tried to adjust to being Claire's father. Belle didn't want him near her initially, especially after learning of his relationship with Willow, a former prostitute. Belle and Shawn finally began to reach an agreement about Claire when she was kidnapped from a diner. This terrified both Belle and Shawn, who then fell under scrutiny from social services. Unbeknownst to anyone, on the occasions when Belle would allow Victor to visit with Claire, she was also spending time with Philip, who had been injured in his duties as a Marine and needed reconstructive surgery.
When the case finally went to court, Philip showed up, having just had a face transplant, and won temporary custody of Claire, who was legally his daughter because he was married to Belle at the time of her birth and was named as her father on the birth certificate. Shortly after, Shawn and Belle kidnapped the little girl and fled the country, with Philip desperate to find out what had happened to the child he'd raised for the first year of her life. Philip was willing to use any methods to get Claire back, including teaming up with E.J. Wells.
Philip began his attempts to win Belle back, but she still maintained her relationship with Shawn. Belle and Philip even became lovers again after her father, John, died, but Belle chose to marry Shawn. When Shawn messed up at a crime scene, Philip offered to do anything he could to help Shawn with his career -- if Belle would sleep with him. Belle agreed to do so, but at the last moment, Philip felt guilty and told her she didn't have to go through with it. Shawn, Belle, and Claire left Salem soon after to bond as a family.
