The incident took place at an address in North East Close, Southampton, between 6.30am and 6.40am.
It is alleged that a woman knocked on the back door and asked to use the toilet and the occupant, a man in his 70s, let her in.
After she left, he realised his blue Huawei P30 mobile phone worth £300 and a gold crucifix necklace worth £100 were missing. The phone’s unique identity number is 868161041502791.
Officers are conducting enquiries and would like to speak to anyone who has information about this incident.
Have you come across these items? Do you know the woman involved?
She is described as:
-aged between 19 and 25
-5ft 6ins tall
-dark brown hair
-having a cold sore
-wearing a dark blouse or jacket, ripped jeans and soft shoes or trainers on the day of the incident
It is believed she may have links to Portsmouth.
Please contact Police on 101 or report online, quoting 44210323338.
Alternatively, you can contact independent charity, Crimestoppers, anonymously on 0800 555 111.