Ответ:
1. Philip lost his camera when he was walking about the city.
2. I bought this nice dress when I was shopping in Moscow.
3. He rang her up when she was having supper.
4. He made these photos when he was seeing sights of St.Peterburg.
5. I saw her last when I was talking with her friend.
6. She heard that song when she was sitting on the bench in the park.
7. They tried national food when they were dining at some exotic restaurant.
8. I looked at these pictures last when I was visiting the Tretyakov Gallery.
9. He called me when I was writing a letter to my foreign friend.
10. I read the book when it was raining.