The offence took place in the gardens of St Peter’s Church, at about 10.45pm on Thursday.
The victim, 17, had his phone stolen after being threatened at knifepoint.
Two men, aged 18 and 21, have been arrested in connection with the offence and released on bail.
Police today (Wednesday) released a CCTV image of a man they are trying to trace in connection with the robbery.
Anyone with information is asked to call Kirklees District CID on 101, quoting crime reference 13180548948.