Most long distance buses arrive into Oslo Bus Terminal. There is a taxi rank by the terminal. If you want to take public transportation you have to walk to Jernbanetorget (by the Central Station). Tram number 12 and 13 and bus number 30, 31 and 32 will take you to Anker. The stop is called Hausmannsgate.
Walking distance from Oslo Bus Terminal to Anker: 7–8 minutes