A man was pushed to the floor and kicked by thugs who stole his iPhone.
The attack happened in Station Road, Hemel Hempstead, close to the junction with Heath Lane, between 1.30am and 2.30am on Sunday, August 2.
Police are appealing for witnesses and information following the robbery and would like to speak to the driver of a taxi who may have seen what happened.
Det Con Andy Roseblade said: “It is believed a large seven seater taxi pulled into Heath Lane around the time of the attack and turned around in the road entrance.
“I would like to identify the driver of this taxi to see if he or she witnessed the incident. If this was you, please contact me as soon as possible via the non-emergency number 101, quoting crime reference D1/15/5015.”
Alternatively contact Crimestoppers, anonymously, on 0800 555 111 or through their anonymous online form at www.crimestoppers-uk.org