British Transport Police arrested a 17-year-old boy after viewing CCTV and tracking the handset to an address.
Officers received reports a woman, in her 30s, had been robbed outside East Ham Underground station at around 2pm on Tuesday.
Despite getting the call an hour later, a force spokesman said detectives “carried out urgent enquiries” and met the victim “before tracking the phone to a residential address”.
He added: “Officers attended, and a teenage boy was arrested on suspicion of robbery.”
BTP said a pregnant woman had been punched in the stomach at East Ham and her phone taken.
“We are committed to making the network a hostile environment for these offenders”, they wrote on X.
London has become the phone snatch capital of Europe with criminals taking 70,137 devices last year - 192 a day or one every seven-and-a-half minutes.
The Metropolitan Police said there is a £50m-a-year trade in snatched handsets across the capital.
London’s most notorious snatcher Sonny Stringer, 28, was jailed last year for stealing 24 phones in one morning.
City of London Police officers used their unmarked Volvo XC90 to knock Stringer off his e-bike as he fled after terrorising victims in the West End.