The robbery was reported around 10 p.m. at Stockton and Clay streets.
The 25-year-old victim was sitting at the bus stop when a suspect approached her from behind, grabbed her phone then ran away, according to police.
The victim suffered a scratch under her nose but declined medical treatment, police said.
The suspect remains at large. Anyone with information about the robbery is encouraged to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.